diff --git a/Doc/lib/libtypes.tex b/Doc/lib/libtypes.tex index b612a0b53c2..07bf35a9186 100644 --- a/Doc/lib/libtypes.tex +++ b/Doc/lib/libtypes.tex @@ -1,871 +1,129 @@ -\section{Built-in Types} -\label{types} +\section{Standard Module \module{types}} +\declaremodule{standard}{types} -The following sections describe the standard types that are built into -the interpreter. These are the numeric types, sequence types, and -several others, including types themselves. There is no explicit -Boolean type; use integers instead. -\indexii{built-in}{types} -\indexii{Boolean}{type} +\modulesynopsis{Names for all built-in types.} -Some operations are supported by several object types; in particular, -all objects can be compared, tested for truth value, and converted to -a string (with the \code{`{\rm \ldots}`} notation). The latter conversion is -implicitly used when an object is written by the \code{print} statement. -\stindex{print} -\subsection{Truth Value Testing} -\label{truth} +This module defines names for all object types that are used by the +standard Python interpreter, but not for the types defined by various +extension modules. It is safe to use \samp{from types import *} --- +the module does not export any names besides the ones listed here. +New names exported by future versions of this module will all end in +\samp{Type}. -Any object can be tested for truth value, for use in an \code{if} or -\code{while} condition or as operand of the Boolean operations below. -The following values are considered false: -\stindex{if} -\stindex{while} -\indexii{truth}{value} -\indexii{Boolean}{operations} -\index{false} - -\setindexsubitem{(Built-in object)} -\begin{itemize} - -\item \code{None} - \ttindex{None} - -\item zero of any numeric type, e.g., \code{0}, \code{0L}, \code{0.0}. - -\item any empty sequence, e.g., \code{''}, \code{()}, \code{[]}. - -\item any empty mapping, e.g., \code{\{\}}. - -\item instances of user-defined classes, if the class defines a - \code{__nonzero__()} or \code{__len__()} method, when that - method returns zero. - -\end{itemize} - -All other values are considered true --- so objects of many types are -always true. -\index{true} - -Operations and built-in functions that have a Boolean result always -return \code{0} for false and \code{1} for true, unless otherwise -stated. (Important exception: the Boolean operations -\samp{or}\opindex{or} and \samp{and}\opindex{and} always return one of -their operands.) - - -\subsection{Boolean Operations} -\label{boolean} - -These are the Boolean operations, ordered by ascending priority: -\indexii{Boolean}{operations} - -\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes} - \lineiii{\var{x} or \var{y}}{if \var{x} is false, then \var{y}, else \var{x}}{(1)} - \lineiii{\var{x} and \var{y}}{if \var{x} is false, then \var{x}, else \var{y}}{(1)} - \hline - \lineiii{not \var{x}}{if \var{x} is false, then \code{1}, else \code{0}}{(2)} -\end{tableiii} -\opindex{and} -\opindex{or} -\opindex{not} - -\noindent -Notes: - -\begin{description} - -\item[(1)] -These only evaluate their second argument if needed for their outcome. - -\item[(2)] -\samp{not} has a lower priority than non-Boolean operators, so e.g. -\code{not a == b} is interpreted as \code{not(a == b)}, and -\code{a == not b} is a syntax error. - -\end{description} - - -\subsection{Comparisons} -\label{comparisons} - -Comparison operations are supported by all objects. They all have the -same priority (which is higher than that of the Boolean operations). -Comparisons can be chained arbitrarily, e.g. \code{x < y <= z} is -equivalent to \code{x < y and y <= z}, except that \code{y} is -evaluated only once (but in both cases \code{z} is not evaluated at -all when \code{x < y} is found to be false). -\indexii{chaining}{comparisons} - -This table summarizes the comparison operations: - -\begin{tableiii}{c|l|c}{code}{Operation}{Meaning}{Notes} - \lineiii{<}{strictly less than}{} - \lineiii{<=}{less than or equal}{} - \lineiii{>}{strictly greater than}{} - \lineiii{>=}{greater than or equal}{} - \lineiii{==}{equal}{} - \lineiii{<>}{not equal}{(1)} - \lineiii{!=}{not equal}{(1)} - \lineiii{is}{object identity}{} - \lineiii{is not}{negated object identity}{} -\end{tableiii} -\indexii{operator}{comparison} -\opindex{==} % XXX *All* others have funny characters < ! > -\opindex{is} -\opindex{is not} - -\noindent -Notes: - -\begin{description} - -\item[(1)] -\code{<>} and \code{!=} are alternate spellings for the same operator. -(I couldn't choose between \ABC{} and \C{}! :-) -\index{ABC language@\ABC{} language} -\index{language!ABC@\ABC{}} -\indexii{C@\C{}}{language} - -\end{description} - -Objects of different types, except different numeric types, never -compare equal; such objects are ordered consistently but arbitrarily -(so that sorting a heterogeneous array yields a consistent result). -Furthermore, some types (e.g., windows) support only a degenerate -notion of comparison where any two objects of that type are unequal. -Again, such objects are ordered arbitrarily but consistently. -\indexii{types}{numeric} -\indexii{objects}{comparing} - -(Implementation note: objects of different types except numbers are -ordered by their type names; objects of the same types that don't -support proper comparison are ordered by their address.) - -Two more operations with the same syntactic priority, \samp{in} and -\samp{not in}, are supported only by sequence types (below). -\opindex{in} -\opindex{not in} - - -\subsection{Numeric Types} -\label{typesnumeric} - -There are four numeric types: \dfn{plain integers}, \dfn{long integers}, -\dfn{floating point numbers}, and \dfn{complex numbers}. -Plain integers (also just called \dfn{integers}) -are implemented using \code{long} in \C{}, which gives them at least 32 -bits of precision. Long integers have unlimited precision. Floating -point numbers are implemented using \code{double} in \C{}. All bets on -their precision are off unless you happen to know the machine you are -working with. -\indexii{numeric}{types} -\indexii{integer}{types} -\indexii{integer}{type} -\indexiii{long}{integer}{type} -\indexii{floating point}{type} -\indexii{complex number}{type} -\indexii{C@\C{}}{language} - -Complex numbers have a real and imaginary part, which are both -implemented using \code{double} in \C{}. To extract these parts from -a complex number \var{z}, use \code{\var{z}.real} and \code{\var{z}.imag}. - -Numbers are created by numeric literals or as the result of built-in -functions and operators. Unadorned integer literals (including hex -and octal numbers) yield plain integers. Integer literals with an \samp{L} -or \samp{l} suffix yield long integers -(\samp{L} is preferred because \samp{1l} looks too much like eleven!). -Numeric literals containing a decimal point or an exponent sign yield -floating point numbers. Appending \samp{j} or \samp{J} to a numeric -literal yields a complex number. -\indexii{numeric}{literals} -\indexii{integer}{literals} -\indexiii{long}{integer}{literals} -\indexii{floating point}{literals} -\indexii{complex number}{literals} -\indexii{hexadecimal}{literals} -\indexii{octal}{literals} - -Python fully supports mixed arithmetic: when a binary arithmetic -operator has operands of different numeric types, the operand with the -``smaller'' type is converted to that of the other, where plain -integer is smaller than long integer is smaller than floating point is -smaller than complex. -Comparisons between numbers of mixed type use the same rule.% -\footnote{As a consequence, the list \code{[1, 2]} is considered equal - to \code{[1.0, 2.0]}, and similar for tuples.} -The functions \code{int()}, \code{long()}, \code{float()}, -and \code{complex()} can be used -to coerce numbers to a specific type. -\index{arithmetic} -\bifuncindex{int} -\bifuncindex{long} -\bifuncindex{float} -\bifuncindex{complex} - -All numeric types support the following operations, sorted by -ascending priority (operations in the same box have the same -priority; all numeric operations have a higher priority than -comparison operations): - -\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes} - \lineiii{\var{x} + \var{y}}{sum of \var{x} and \var{y}}{} - \lineiii{\var{x} - \var{y}}{difference of \var{x} and \var{y}}{} - \hline - \lineiii{\var{x} * \var{y}}{product of \var{x} and \var{y}}{} - \lineiii{\var{x} / \var{y}}{quotient of \var{x} and \var{y}}{(1)} - \lineiii{\var{x} \%{} \var{y}}{remainder of \code{\var{x} / \var{y}}}{} - \hline - \lineiii{-\var{x}}{\var{x} negated}{} - \lineiii{+\var{x}}{\var{x} unchanged}{} - \hline - \lineiii{abs(\var{x})}{absolute value or magnitude of \var{x}}{} - \lineiii{int(\var{x})}{\var{x} converted to integer}{(2)} - \lineiii{long(\var{x})}{\var{x} converted to long integer}{(2)} - \lineiii{float(\var{x})}{\var{x} converted to floating point}{} - \lineiii{complex(\var{re},\var{im})}{a complex number with real part \var{re}, imaginary part \var{im}. \var{im} defaults to zero.}{} - \lineiii{divmod(\var{x}, \var{y})}{the pair \code{(\var{x} / \var{y}, \var{x} \%{} \var{y})}}{(3)} - \lineiii{pow(\var{x}, \var{y})}{\var{x} to the power \var{y}}{} - \lineiii{\var{x} ** \var{y}}{\var{x} to the power \var{y}}{} -\end{tableiii} -\indexiii{operations on}{numeric}{types} - -\noindent -Notes: -\begin{description} - -\item[(1)] -For (plain or long) integer division, the result is an integer. -The result is always rounded towards minus infinity: 1/2 is 0, -(-1)/2 is -1, 1/(-2) is -1, and (-1)/(-2) is 0. -\indexii{integer}{division} -\indexiii{long}{integer}{division} - -\item[(2)] -Conversion from floating point to (long or plain) integer may round or -truncate as in \C{}; see functions \code{floor()} and \code{ceil()} in -module \code{math} for well-defined conversions. -\bifuncindex{floor} -\bifuncindex{ceil} -\indexii{numeric}{conversions} -\refbimodindex{math} -\indexii{C@\C{}}{language} - -\item[(3)] -See the section on built-in functions for an exact definition. - -\end{description} -% XXXJH exceptions: overflow (when? what operations?) zerodivision - -\subsubsection{Bit-string Operations on Integer Types} -\nodename{Bit-string Operations} - -Plain and long integer types support additional operations that make -sense only for bit-strings. Negative numbers are treated as their 2's -complement value (for long integers, this assumes a sufficiently large -number of bits that no overflow occurs during the operation). - -The priorities of the binary bit-wise operations are all lower than -the numeric operations and higher than the comparisons; the unary -operation \samp{\~} has the same priority as the other unary numeric -operations (\samp{+} and \samp{-}). - -This table lists the bit-string operations sorted in ascending -priority (operations in the same box have the same priority): - -\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes} - \lineiii{\var{x} | \var{y}}{bitwise \dfn{or} of \var{x} and \var{y}}{} - \lineiii{\var{x} \^{} \var{y}}{bitwise \dfn{exclusive or} of \var{x} and \var{y}}{} - \lineiii{\var{x} \&{} \var{y}}{bitwise \dfn{and} of \var{x} and \var{y}}{} - \lineiii{\var{x} << \var{n}}{\var{x} shifted left by \var{n} bits}{(1), (2)} - \lineiii{\var{x} >> \var{n}}{\var{x} shifted right by \var{n} bits}{(1), (3)} - \hline - \lineiii{\~\var{x}}{the bits of \var{x} inverted}{} -\end{tableiii} -\indexiii{operations on}{integer}{types} -\indexii{bit-string}{operations} -\indexii{shifting}{operations} -\indexii{masking}{operations} - -\noindent -Notes: -\begin{description} -\item[(1)] Negative shift counts are illegal and cause a -\exception{ValueError} to be raised. -\item[(2)] A left shift by \var{n} bits is equivalent to -multiplication by \code{pow(2, \var{n})} without overflow check. -\item[(3)] A right shift by \var{n} bits is equivalent to -division by \code{pow(2, \var{n})} without overflow check. -\end{description} - - -\subsection{Sequence Types} -\label{typesseq} - -There are three sequence types: strings, lists and tuples. - -Strings literals are written in single or double quotes: -\code{'xyzzy'}, \code{"frobozz"}. See Chapter 2 of the \emph{Python -Reference Manual} for more about string literals. Lists are -constructed with square brackets, separating items with commas: -\code{[a, b, c]}. Tuples are constructed by the comma operator (not -within square brackets), with or without enclosing parentheses, but an -empty tuple must have the enclosing parentheses, e.g., -\code{a, b, c} or \code{()}. A single item tuple must have a trailing -comma, e.g., \code{(d,)}. -\indexii{sequence}{types} -\indexii{string}{type} -\indexii{tuple}{type} -\indexii{list}{type} - -Sequence types support the following operations. The \samp{in} and -\samp{not in} operations have the same priorities as the comparison -operations. The \samp{+} and \samp{*} operations have the same -priority as the corresponding numeric operations.\footnote{They must -have since the parser can't tell the type of the operands.} - -This table lists the sequence operations sorted in ascending priority -(operations in the same box have the same priority). In the table, -\var{s} and \var{t} are sequences of the same type; \var{n}, \var{i} -and \var{j} are integers: - -\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes} - \lineiii{\var{x} in \var{s}}{\code{1} if an item of \var{s} is equal to \var{x}, else \code{0}}{} - \lineiii{\var{x} not in \var{s}}{\code{0} if an item of \var{s} is -equal to \var{x}, else \code{1}}{} - \hline - \lineiii{\var{s} + \var{t}}{the concatenation of \var{s} and \var{t}}{} - \lineiii{\var{s} * \var{n}{\rm ,} \var{n} * \var{s}}{\var{n} copies of \var{s} concatenated}{(3)} - \hline - \lineiii{\var{s}[\var{i}]}{\var{i}'th item of \var{s}, origin 0}{(1)} - \lineiii{\var{s}[\var{i}:\var{j}]}{slice of \var{s} from \var{i} to \var{j}}{(1), (2)} - \hline - \lineiii{len(\var{s})}{length of \var{s}}{} - \lineiii{min(\var{s})}{smallest item of \var{s}}{} - \lineiii{max(\var{s})}{largest item of \var{s}}{} -\end{tableiii} -\indexiii{operations on}{sequence}{types} -\bifuncindex{len} -\bifuncindex{min} -\bifuncindex{max} -\indexii{concatenation}{operation} -\indexii{repetition}{operation} -\indexii{subscript}{operation} -\indexii{slice}{operation} -\opindex{in} -\opindex{not in} - -\noindent -Notes: - -\begin{description} - -\item[(1)] If \var{i} or \var{j} is negative, the index is relative to - the end of the string, i.e., \code{len(\var{s}) + \var{i}} or - \code{len(\var{s}) + \var{j}} is substituted. But note that \code{-0} is - still \code{0}. - -\item[(2)] The slice of \var{s} from \var{i} to \var{j} is defined as - the sequence of items with index \var{k} such that \code{\var{i} <= - \var{k} < \var{j}}. If \var{i} or \var{j} is greater than - \code{len(\var{s})}, use \code{len(\var{s})}. If \var{i} is omitted, - use \code{0}. If \var{j} is omitted, use \code{len(\var{s})}. If - \var{i} is greater than or equal to \var{j}, the slice is empty. - -\item[(3)] Values of \var{n} less than \code{0} are treated as - \code{0} (which yields an empty sequence of the same type as - \var{s}). - -\end{description} - -\subsubsection{More String Operations} - -String objects have one unique built-in operation: the \code{\%} -operator (modulo) with a string left argument interprets this string -as a \C{} \cfunction{sprintf()} format string to be applied to the -right argument, and returns the string resulting from this formatting -operation. - -The right argument should be a tuple with one item for each argument -required by the format string; if the string requires a single -argument, the right argument may also be a single non-tuple object.% -\footnote{A tuple object in this case should be a singleton.} -The following format characters are understood: -\code{\%}, \code{c}, \code{s}, \code{i}, \code{d}, \code{u}, \code{o}, -\code{x}, \code{X}, \code{e}, \code{E}, \code{f}, \code{g}, \code{G}. -Width and precision may be a \code{*} to specify that an integer argument -specifies the actual width or precision. The flag characters -\code{-}, \code{+}, blank, \code{\#} and \code{0} are understood. The -size specifiers \code{h}, \code{l} or \code{L} may be -present but are ignored. The \code{\%s} conversion takes any Python -object and converts it to a string using \code{str()} before -formatting it. The ANSI features \code{\%p} and \code{\%n} -are not supported. Since Python strings have an explicit length, -\code{\%s} conversions don't assume that \code{'\e0'} is the end of -the string. - -For safety reasons, floating point precisions are clipped to 50; -\code{\%f} conversions for numbers whose absolute value is over 1e25 -are replaced by \code{\%g} conversions.% -\footnote{These numbers are fairly arbitrary. They are intended to -avoid printing endless strings of meaningless digits without hampering -correct use and without having to know the exact precision of floating -point values on a particular machine.} -All other errors raise exceptions. - -If the right argument is a dictionary (or any kind of mapping), then -the formats in the string must have a parenthesized key into that -dictionary inserted immediately after the \character{\%} character, -and each format formats the corresponding entry from the mapping. -For example: +Typical use is for functions that do different things depending on +their argument types, like the following: \begin{verbatim} ->>> count = 2 ->>> language = 'Python' ->>> print '%(language)s has %(count)03d quote types.' % vars() -Python has 002 quote types. +from types import * +def delete(list, item): + if type(item) is IntType: + del list[item] + else: + list.remove(item) \end{verbatim} -In this case no \code{*} specifiers may occur in a format (since they -require a sequential parameter list). - -Additional string operations are defined in standard module -\module{string} and in built-in module \module{re}. -\refstmodindex{string} -\refbimodindex{re} - -\subsubsection{Mutable Sequence Types} - -List objects support additional operations that allow in-place -modification of the object. -These operations would be supported by other mutable sequence types -(when added to the language) as well. -Strings and tuples are immutable sequence types and such objects cannot -be modified once created. -The following operations are defined on mutable sequence types (where -\var{x} is an arbitrary object): -\indexiii{mutable}{sequence}{types} -\indexii{list}{type} - -\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes} - \lineiii{\var{s}[\var{i}] = \var{x}} - {item \var{i} of \var{s} is replaced by \var{x}}{} - \lineiii{\var{s}[\var{i}:\var{j}] = \var{t}} - {slice of \var{s} from \var{i} to \var{j} is replaced by \var{t}}{} - \lineiii{del \var{s}[\var{i}:\var{j}]} - {same as \code{\var{s}[\var{i}:\var{j}] = []}}{} - \lineiii{\var{s}.append(\var{x})} - {same as \code{\var{s}[len(\var{s}):len(\var{s})] = [\var{x}]}}{} - \lineiii{\var{s}.count(\var{x})} - {return number of \var{i}'s for which \code{\var{s}[\var{i}] == \var{x}}}{} - \lineiii{\var{s}.index(\var{x})} - {return smallest \var{i} such that \code{\var{s}[\var{i}] == \var{x}}}{(1)} - \lineiii{\var{s}.insert(\var{i}, \var{x})} - {same as \code{\var{s}[\var{i}:\var{i}] = [\var{x}]} - if \code{\var{i} >= 0}}{} - \lineiii{\var{s}.pop(\optional{\var{i}})} - {same as \code{\var{x} = \var{s}[\var{i}]; del \var{s}[\var{i}]; return \var{x}}}{(4)} - \lineiii{\var{s}.remove(\var{x})} - {same as \code{del \var{s}[\var{s}.index(\var{x})]}}{(1)} - \lineiii{\var{s}.reverse()} - {reverses the items of \var{s} in place}{(3)} - \lineiii{\var{s}.sort(\optional{\var{cmpfunc}})} - {sort the items of \var{s} in place}{(2), (3)} -\end{tableiii} -\indexiv{operations on}{mutable}{sequence}{types} -\indexiii{operations on}{sequence}{types} -\indexiii{operations on}{list}{type} -\indexii{subscript}{assignment} -\indexii{slice}{assignment} -\stindex{del} -\setindexsubitem{(list method)} -\ttindex{append} -\ttindex{count} -\ttindex{index} -\ttindex{insert} -\ttindex{pop} -\ttindex{remove} -\ttindex{reverse} -\ttindex{sort} - -\noindent -Notes: -\begin{description} -\item[(1)] Raises an exception when \var{x} is not found in \var{s}. - -\item[(2)] The \code{sort()} method takes an optional argument - specifying a comparison function of two arguments (list items) which - should return \code{-1}, \code{0} or \code{1} depending on whether the - first argument is considered smaller than, equal to, or larger than the - second argument. Note that this slows the sorting process down - considerably; e.g. to sort a list in reverse order it is much faster - to use calls to \code{sort()} and \code{reverse()} than to use - \code{sort()} with a comparison function that reverses the ordering of - the elements. - -\item[(3)] The \code{sort()} and \code{reverse()} methods modify the -list in place for economy of space when sorting or reversing a large -list. They don't return the sorted or reversed list to remind you of -this side effect. - -\item[(4)] The \method{pop()} method is experimental and not supported -by other mutable sequence types than lists. -The optional argument \var{i} defaults to \code{-1}, so that -by default the last item is removed and returned. - -\end{description} - - -\subsection{Mapping Types} -\label{typesmapping} - -A \dfn{mapping} object maps values of one type (the key type) to -arbitrary objects. Mappings are mutable objects. There is currently -only one standard mapping type, the \dfn{dictionary}. A dictionary's keys are -almost arbitrary values. The only types of values not acceptable as -keys are values containing lists or dictionaries or other mutable -types that are compared by value rather than by object identity. -Numeric types used for keys obey the normal rules for numeric -comparison: if two numbers compare equal (e.g. \code{1} and -\code{1.0}) then they can be used interchangeably to index the same -dictionary entry. - -\indexii{mapping}{types} -\indexii{dictionary}{type} - -Dictionaries are created by placing a comma-separated list of -\code{\var{key}: \var{value}} pairs within braces, for example: -\code{\{'jack': 4098, 'sjoerd': 4127\}} or -\code{\{4098: 'jack', 4127: 'sjoerd'\}}. - -The following operations are defined on mappings (where \var{a} is a -mapping, \var{k} is a key and \var{x} is an arbitrary object): - -\begin{tableiii}{c|l|c}{code}{Operation}{Result}{Notes} - \lineiii{len(\var{a})}{the number of items in \var{a}}{} - \lineiii{\var{a}[\var{k}]}{the item of \var{a} with key \var{k}}{(1)} - \lineiii{\var{a}[\var{k}] = \var{x}}{set \code{\var{a}[\var{k}]} to \var{x}}{} - \lineiii{del \var{a}[\var{k}]}{remove \code{\var{a}[\var{k}]} from \var{a}}{(1)} - \lineiii{\var{a}.clear()}{remove all items from \code{a}}{} - \lineiii{\var{a}.copy()}{a (shallow) copy of \code{a}}{} - \lineiii{\var{a}.has_key(\var{k})}{\code{1} if \var{a} has a key \var{k}, else \code{0}}{} - \lineiii{\var{a}.items()}{a copy of \var{a}'s list of (key, item) pairs}{(2)} - \lineiii{\var{a}.keys()}{a copy of \var{a}'s list of keys}{(2)} - \lineiii{\var{a}.update(\var{b})}{\code{for k, v in \var{b}.items(): \var{a}[k] = v}}{(3)} - \lineiii{\var{a}.values()}{a copy of \var{a}'s list of values}{(2)} - \lineiii{\var{a}.get(\var{k}\optional{, \var{f}})}{the item of \var{a} with key \var{k}}{(4)} -\end{tableiii} -\indexiii{operations on}{mapping}{types} -\indexiii{operations on}{dictionary}{type} -\stindex{del} -\bifuncindex{len} -\setindexsubitem{(dictionary method)} -\ttindex{keys} -\ttindex{has_key} - -\noindent -Notes: -\begin{description} -\item[(1)] Raises an exception if \var{k} is not in the map. - -\item[(2)] Keys and values are listed in random order. - -\item[(3)] \var{b} must be of the same type as \var{a}. - -\item[(4)] Never raises an exception if \var{k} is not in the map, -instead it returns \var{f}. \var{f} is optional, when not provided -and \var{k} is not in the map, \code{None} is returned. -\end{description} - - -\subsection{Other Built-in Types} -\label{typesother} - -The interpreter supports several other kinds of objects. -Most of these support only one or two operations. - -\subsubsection{Modules} - -The only special operation on a module is attribute access: -\code{\var{m}.\var{name}}, where \var{m} is a module and \var{name} -accesses a name defined in \var{m}'s symbol table. Module attributes -can be assigned to. (Note that the \code{import} statement is not, -strictly spoking, an operation on a module object; \code{import -\var{foo}} does not require a module object named \var{foo} to exist, -rather it requires an (external) \emph{definition} for a module named -\var{foo} somewhere.) - -A special member of every module is \code{__dict__}. -This is the dictionary containing the module's symbol table. -Modifying this dictionary will actually change the module's symbol -table, but direct assignment to the \code{__dict__} attribute is not -possible (i.e., you can write \code{\var{m}.__dict__['a'] = 1}, which -defines \code{\var{m}.a} to be \code{1}, but you can't write -\code{\var{m}.__dict__ = \{\}}. - -Modules are written like this: \code{}. - -\subsubsection{Classes and Class Instances} -\nodename{Classes and Instances} - -See Chapters 3 and 7 of the \emph{Python Reference Manual} for these. - -\subsubsection{Functions} - -Function objects are created by function definitions. The only -operation on a function object is to call it: -\code{\var{func}(\var{argument-list})}. - -There are really two flavors of function objects: built-in functions -and user-defined functions. Both support the same operation (to call -the function), but the implementation is different, hence the -different object types. - -The implementation adds two special read-only attributes: -\code{\var{f}.func_code} is a function's \dfn{code -object}\obindex{code} (see below) and \code{\var{f}.func_globals} is -the dictionary used as the function's global name space (this is the -same as \code{\var{m}.__dict__} where \var{m} is the module in which -the function \var{f} was defined). - - -\subsubsection{Methods} -\obindex{method} - -Methods are functions that are called using the attribute notation. -There are two flavors: built-in methods (such as \code{append()} on -lists) and class instance methods. Built-in methods are described -with the types that support them. - -The implementation adds two special read-only attributes to class -instance methods: \code{\var{m}.im_self} is the object whose method this -is, and \code{\var{m}.im_func} is the function implementing the method. -Calling \code{\var{m}(\var{arg-1}, \var{arg-2}, {\rm \ldots}, -\var{arg-n})} is completely equivalent to calling -\code{\var{m}.im_func(\var{m}.im_self, \var{arg-1}, \var{arg-2}, {\rm -\ldots}, \var{arg-n})}. - -See the \emph{Python Reference Manual} for more information. - -\subsubsection{Code Objects} -\obindex{code} - -Code objects are used by the implementation to represent -``pseudo-compiled'' executable Python code such as a function body. -They differ from function objects because they don't contain a -reference to their global execution environment. Code objects are -returned by the built-in \code{compile()} function and can be -extracted from function objects through their \code{func_code} -attribute. -\bifuncindex{compile} -\ttindex{func_code} - -A code object can be executed or evaluated by passing it (instead of a -source string) to the \code{exec} statement or the built-in -\code{eval()} function. -\stindex{exec} -\bifuncindex{eval} - -See the \emph{Python Reference Manual} for more information. - -\subsubsection{Type Objects} -\label{bltin-type-objects} - -Type objects represent the various object types. An object's type is -accessed by the built-in function \code{type()}. There are no special -operations on types. The standard module \code{types} defines names -for all standard built-in types. -\bifuncindex{type} -\refstmodindex{types} - -Types are written like this: \code{}. - -\subsubsection{The Null Object} -\label{bltin-null-object} - -This object is returned by functions that don't explicitly return a -value. It supports no special operations. There is exactly one null -object, named \code{None} (a built-in name). - -It is written as \code{None}. - -\subsubsection{File Objects} -\label{bltin-file-objects} - -File objects are implemented using \C{}'s \code{stdio} package and can be -created with the built-in function \code{open()} described under -Built-in Functions below. They are also returned by some other -built-in functions and methods, e.g.\ \code{posix.popen()} and -\code{posix.fdopen()} and the \code{makefile()} method of socket -objects. -\bifuncindex{open} -\refbimodindex{posix} -\refbimodindex{socket} - -When a file operation fails for an I/O-related reason, the exception -\code{IOError} is raised. This includes situations where the -operation is not defined for some reason, like \code{seek()} on a tty -device or writing a file opened for reading. - -Files have the following methods: - - -\begin{methoddesc}[file]{close}{} - Close the file. A closed file cannot be read or written anymore. -\end{methoddesc} - -\begin{methoddesc}[file]{flush}{} - Flush the internal buffer, like \code{stdio}'s \code{fflush()}. -\end{methoddesc} - -\begin{methoddesc}[file]{isatty}{} - Return \code{1} if the file is connected to a tty(-like) device, else - \code{0}. -\end{methoddesc} - -\begin{methoddesc}[file]{fileno}{} -Return the integer ``file descriptor'' that is used by the underlying -implementation to request I/O operations from the operating system. -This can be useful for other, lower level interfaces that use file -descriptors, e.g. module \code{fcntl} or \code{os.read()} and friends. -\refbimodindex{fcntl} -\end{methoddesc} - -\begin{methoddesc}[file]{read}{\optional{size}} - Read at most \var{size} bytes from the file (less if the read hits - \EOF{} or no more data is immediately available on a pipe, tty or - similar device). If the \var{size} argument is negative or omitted, - read all data until \EOF{} is reached. The bytes are returned as a string - object. An empty string is returned when \EOF{} is encountered - immediately. (For certain files, like ttys, it makes sense to - continue reading after an \EOF{} is hit.) -\end{methoddesc} - -\begin{methoddesc}[file]{readline}{\optional{size}} - Read one entire line from the file. A trailing newline character is - kept in the string% -\footnote{The advantage of leaving the newline on is that an empty string - can be returned to mean \EOF{} without being ambiguous. Another - advantage is that (in cases where it might matter, e.g. if you - want to make an exact copy of a file while scanning its lines) - you can tell whether the last line of a file ended in a newline - or not (yes this happens!).} - (but may be absent when a file ends with an - incomplete line). If the \var{size} argument is present and - non-negative, it is a maximum byte count (including the trailing - newline) and an incomplete line may be returned. - An empty string is returned when \EOF{} is hit - immediately. Note: unlike \code{stdio}'s \cfunction{fgets()}, the returned - string contains null characters (\code{'\e 0'}) if they occurred in the - input. -\end{methoddesc} - -\begin{methoddesc}[file]{readlines}{\optional{sizehint}} - Read until \EOF{} using \method{readline()} and return a list containing - the lines thus read. If the optional \var{sizehint} argument is - present, instead of reading up to \EOF{}, whole lines totalling - approximately \var{sizehint} bytes (possibly after rounding up to an - internal buffer size) are read. -\end{methoddesc} - -\begin{methoddesc}[file]{seek}{offset\optional{, whence}} - Set the file's current position, like \code{stdio}'s \cfunction{fseek()}. - The \var{whence} argument is optional and defaults to \code{0} - (absolute file positioning); other values are \code{1} (seek - relative to the current position) and \code{2} (seek relative to the - file's end). There is no return value. -\end{methoddesc} - -\begin{methoddesc}[file]{tell}{} - Return the file's current position, like \code{stdio}'s - \cfunction{ftell()}. -\end{methoddesc} - -\begin{methoddesc}[file]{truncate}{\optional{size}} -Truncate the file's size. If the optional size argument present, the -file is truncated to (at most) that size. The size defaults to the -current position. Availability of this function depends on the -operating system version (e.g., not all \UNIX{} versions support this -operation). -\end{methoddesc} - -\begin{methoddesc}[file]{write}{str} -Write a string to the file. There is no return value. Note: due to -buffering, the string may not actually show up in the file until -the \method{flush()} or \method{close()} method is called. -\end{methoddesc} - -\begin{methoddesc}[file]{writelines}{list} -Write a list of strings to the file. There is no return value. -(The name is intended to match \method{readlines()}; -\method{writelines()} does not add line separators.) -\end{methoddesc} - - -File objects also offer the following attributes: - -\begin{memberdesc}[file]{closed} -Boolean indicating the current state of the file object. This is a -read-only attribute; the \method{close()} method changes the value. -\end{memberdesc} - -\begin{memberdesc}[file]{mode} -The I/O mode for the file. If the file was created using the -\function{open()} built-in function, this will be the value of the -\var{mode} parameter. This is a read-only attribute. -\end{memberdesc} - -\begin{memberdesc}[file]{name} -If the file object was created using \function{open()}, the name of -the file. Otherwise, some string that indicates the source of the -file object, of the form \samp{<\mbox{\ldots}>}. This is a read-only -attribute. -\end{memberdesc} - -\begin{memberdesc}[file]{softspace} -Boolean that indicates whether a space character needs to be printed -before another value when using the \keyword{print} statement. -Classes that are trying to simulate a file object should also have a -writable \member{softspace} attribute, which should be initialized to -zero. This will be automatic for classes implemented in Python; types -implemented in \C{} will have to provide a writable \member{softspace} -attribute. -\end{memberdesc} - -\subsubsection{Internal Objects} - -See the \emph{Python Reference Manual} for this information. It -describes code objects, stack frame objects, traceback objects, and -slice objects. - - -\subsection{Special Attributes} -\label{specialattrs} - -The implementation adds a few special read-only attributes to several -object types, where they are relevant: - -\begin{itemize} - -\item -\code{\var{x}.__dict__} is a dictionary of some sort used to store an -object's (writable) attributes; - -\item -\code{\var{x}.__methods__} lists the methods of many built-in object types, -e.g., \code{[].__methods__} yields -\code{['append', 'count', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']}; - -\item -\code{\var{x}.__members__} lists data attributes; - -\item -\code{\var{x}.__class__} is the class to which a class instance belongs; - -\item -\code{\var{x}.__bases__} is the tuple of base classes of a class object. - -\end{itemize} +The module defines the following names: + +\begin{datadesc}{NoneType} +The type of \code{None}. +\end{datadesc} + +\begin{datadesc}{TypeType} +The type of type objects (such as returned by +\function{type()}\bifuncindex{type}). +\end{datadesc} + +\begin{datadesc}{IntType} +The type of integers (e.g. \code{1}). +\end{datadesc} + +\begin{datadesc}{LongType} +The type of long integers (e.g. \code{1L}). +\end{datadesc} + +\begin{datadesc}{FloatType} +The type of floating point numbers (e.g. \code{1.0}). +\end{datadesc} + +\begin{datadesc}{StringType} +The type of character strings (e.g. \code{'Spam'}). +\end{datadesc} + +\begin{datadesc}{TupleType} +The type of tuples (e.g. \code{(1, 2, 3, 'Spam')}). +\end{datadesc} + +\begin{datadesc}{ListType} +The type of lists (e.g. \code{[0, 1, 2, 3]}). +\end{datadesc} + +\begin{datadesc}{DictType} +The type of dictionaries (e.g. \code{\{'Bacon': 1, 'Ham': 0\}}). +\end{datadesc} + +\begin{datadesc}{DictionaryType} +An alternate name for \code{DictType}. +\end{datadesc} + +\begin{datadesc}{FunctionType} +The type of user-defined functions and lambdas. +\end{datadesc} + +\begin{datadesc}{LambdaType} +An alternate name for \code{FunctionType}. +\end{datadesc} + +\begin{datadesc}{CodeType} +The type for code objects such as returned by +\function{compile()}\bifuncindex{compile}. +\end{datadesc} + +\begin{datadesc}{ClassType} +The type of user-defined classes. +\end{datadesc} + +\begin{datadesc}{InstanceType} +The type of instances of user-defined classes. +\end{datadesc} + +\begin{datadesc}{MethodType} +The type of methods of user-defined class instances. +\end{datadesc} + +\begin{datadesc}{UnboundMethodType} +An alternate name for \code{MethodType}. +\end{datadesc} + +\begin{datadesc}{BuiltinFunctionType} +The type of built-in functions like \function{len()} or +\function{sys.exit()}. +\end{datadesc} + +\begin{datadesc}{BuiltinMethodType} +An alternate name for \code{BuiltinFunction}. +\end{datadesc} + +\begin{datadesc}{ModuleType} +The type of modules. +\end{datadesc} + +\begin{datadesc}{FileType} +The type of open file objects such as \code{sys.stdout}. +\end{datadesc} + +\begin{datadesc}{XRangeType} +The type of range objects returned by +\function{xrange()}\bifuncindex{xrange}. +\end{datadesc} + +\begin{datadesc}{TracebackType} +The type of traceback objects such as found in +\code{sys.exc_traceback}. +\end{datadesc} + +\begin{datadesc}{FrameType} +The type of frame objects such as found in \code{tb.tb_frame} if +\code{tb} is a traceback object. +\end{datadesc}