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#14097: merge with 3.3.

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Ezio Melotti 2013-05-20 08:14:14 +03:00
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Doc/tutorial/introduction.rst
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@ -5,7 +5,7 @@ An Informal Introduction to Python
********************************** **********************************
In the following examples, input and output are distinguished by the presence or In the following examples, input and output are distinguished by the presence or
absence of prompts (``>>>`` and ``...``): to repeat the example, you must type absence of prompts (:term:`>>>` and :term:`...`): to repeat the example, you must type
everything after the prompt, when the prompt appears; lines that do not begin everything after the prompt, when the prompt appears; lines that do not begin
with a prompt are output from the interpreter. Note that a secondary prompt on a with a prompt are output from the interpreter. Note that a secondary prompt on a
line by itself in an example means you must type a blank line; this is used to line by itself in an example means you must type a blank line; this is used to
@ -22,9 +22,9 @@ be omitted when typing in examples.
Some examples:: Some examples::
# this is the first comment # this is the first comment
SPAM = 1 # and this is the second comment spam = 1 # and this is the second comment
# ... and now a third! # ... and now a third!
STRING = "# This is not a comment." text = "# This is not a comment because it's inside quotes."
.. _tut-calculator: .. _tut-calculator:
@ -44,55 +44,53 @@ Numbers
The interpreter acts as a simple calculator: you can type an expression at it The interpreter acts as a simple calculator: you can type an expression at it
and it will write the value. Expression syntax is straightforward: the and it will write the value. Expression syntax is straightforward: the
operators ``+``, ``-``, ``*`` and ``/`` work just like in most other languages operators ``+``, ``-``, ``*`` and ``/`` work just like in most other languages
(for example, Pascal or C); parentheses can be used for grouping. For example:: (for example, Pascal or C); parentheses (``()``) can be used for grouping.
For example::
>>> 2+2 >>> 2 + 2
4 4
>>> # This is a comment >>> 50 - 5*6
... 2+2 20
4 >>> (50 - 5*6) / 4
>>> 2+2 # and a comment on the same line as code
4
>>> (50-5*6)/4
5.0 5.0
>>> 8/5 # Fractions aren't lost when dividing integers >>> 8 / 5 # division always returns a floating point number
1.6 1.6
Note: You might not see exactly the same result; floating point results can The integer numbers (e.g. ``2``, ``4``, ``20``) have type :class:`int`,
differ from one machine to another. We will say more later about controlling the ones with a fractional part (e.g. ``5.0``, ``1.6``) have type
the appearance of floating point output. See also :ref:`tut-fp-issues` for a :class:`float`. We will see more about numberic types later in the tutorial.
full discussion of some of the subtleties of floating point numbers and their
representations.
To do integer division and get an integer result, Division (``/``) always returns a float. To do :term:`floor division` and
discarding any fractional result, there is another operator, ``//``:: get an integer result (discarding any fractional result) you can use the ``//``
operator; to calculate the remainder you can use ``%``::
>>> # Integer division returns the floor: >>> 17 / 3 # classic division returns a float
... 7//3 5.666666666666667
>>>
>>> 17 // 3 # floor division discards the fractional part
5
>>> 17 % 3 # the % operator returns the remainder of the division
2 2
>>> 7//-3 >>> 5 * 3 + 2 # result * divisor + remainder
-3 17
The equal sign (``'='``) is used to assign a value to a variable. Afterwards, no With Python is possible to use the ``**`` operator to calculate powers [#]_::
>>> 5 ** 2 # 5 squared
25
>>> 2 ** 7 # 2 to the power of 7
128
The equal sign (``=``) is used to assign a value to a variable. Afterwards, no
result is displayed before the next interactive prompt:: result is displayed before the next interactive prompt::
>>> width = 20 >>> width = 20
>>> height = 5*9 >>> height = 5 * 9
>>> width * height >>> width * height
900 900
A value can be assigned to several variables simultaneously:: If a variable is not "defined" (assigned a value), trying to use it will
give you an error::
>>> x = y = z = 0 # Zero x, y and z
>>> x
0
>>> y
0
>>> z
0
Variables must be "defined" (assigned a value) before they can be used, or an
error will occur::
>>> n # try to access an undefined variable >>> n # try to access an undefined variable
Traceback (most recent call last): Traceback (most recent call last):
@ -107,49 +105,6 @@ convert the integer operand to floating point::
>>> 7.0 / 2 >>> 7.0 / 2
3.5 3.5
Complex numbers are also supported; imaginary numbers are written with a suffix
of ``j`` or ``J``. Complex numbers with a nonzero real component are written as
``(real+imagj)``, or can be created with the ``complex(real, imag)`` function.
::
>>> 1j * 1J
(-1+0j)
>>> 1j * complex(0, 1)
(-1+0j)
>>> 3+1j*3
(3+3j)
>>> (3+1j)*3
(9+3j)
>>> (1+2j)/(1+1j)
(1.5+0.5j)
Complex numbers are always represented as two floating point numbers, the real
and imaginary part. To extract these parts from a complex number *z*, use
``z.real`` and ``z.imag``. ::
>>> a=1.5+0.5j
>>> a.real
1.5
>>> a.imag
0.5
The conversion functions to floating point and integer (:func:`float`,
:func:`int`) don't work for complex numbers --- there is not one correct way to
convert a complex number to a real number. Use ``abs(z)`` to get its magnitude
(as a float) or ``z.real`` to get its real part::
>>> a=3.0+4.0j
>>> float(a)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: can't convert complex to float; use abs(z)
>>> a.real
3.0
>>> a.imag
4.0
>>> abs(a) # sqrt(a.real**2 + a.imag**2)
5.0
In interactive mode, the last printed expression is assigned to the variable In interactive mode, the last printed expression is assigned to the variable
``_``. This means that when you are using Python as a desk calculator, it is ``_``. This means that when you are using Python as a desk calculator, it is
somewhat easier to continue calculations, for example:: somewhat easier to continue calculations, for example::
@ -167,20 +122,28 @@ This variable should be treated as read-only by the user. Don't explicitly
assign a value to it --- you would create an independent local variable with the assign a value to it --- you would create an independent local variable with the
same name masking the built-in variable with its magic behavior. same name masking the built-in variable with its magic behavior.
In addition to :class:`int` and :class:`float`, Python supports other types of
numbers, such as :class:`~decimal.Decimal` and :class:`~fractions.Fraction`.
Python also has built-in support for :ref:`complex numbers <typesnumeric>`,
and uses the ``j`` or ``J`` suffix to indicate the imaginary part
(e.g. ``3+5j``).
.. _tut-strings: .. _tut-strings:
Strings Strings
------- -------
Besides numbers, Python can also manipulate strings, which can be expressed in Besides numbers, Python can also manipulate strings, which can be expressed
several ways. They can be enclosed in single quotes or double quotes:: in several ways. They can be enclosed in single quotes (``'...'``) or
double quotes (``"..."``) with the same result [#]_. ``\`` can be used
to escape quotes::
>>> 'spam eggs' >>> 'spam eggs' # single quotes
'spam eggs' 'spam eggs'
>>> 'doesn\'t' >>> 'doesn\'t' # use \' to escape the single quote...
"doesn't" "doesn't"
>>> "doesn't" >>> "doesn't" # ...or use double quotes instead
"doesn't" "doesn't"
>>> '"Yes," he said.' >>> '"Yes," he said.'
'"Yes," he said.' '"Yes," he said.'
@ -189,38 +152,40 @@ several ways. They can be enclosed in single quotes or double quotes::
>>> '"Isn\'t," she said.' >>> '"Isn\'t," she said.'
'"Isn\'t," she said.' '"Isn\'t," she said.'
The interpreter prints the result of string operations in the same way as they In the interactive interpreter, the output string is enclosed in quotes and
are typed for input: inside quotes, and with quotes and other funny characters special characters are escaped with backslashes. While this might sometimes
escaped by backslashes, to show the precise value. The string is enclosed in look different from the input (the enclosing quotes could change), the two
double quotes if the string contains a single quote and no double quotes, else strings are equivalent. The string is enclosed in double quotes if
it's enclosed in single quotes. The :func:`print` function produces a more the string contains a single quote and no double quotes, otherwise it is
readable output for such input strings. enclosed in single quotes. The :func:`print` function produces a more
readable output, by omitting the enclosing quotes and by printing escaped
and special characters::
String literals can span multiple lines in several ways. Continuation lines can >>> '"Isn\'t," she said.'
be used, with a backslash as the last character on the line indicating that the '"Isn\'t," she said.'
next line is a logical continuation of the line:: >>> print('"Isn\'t," she said.')
"Isn't," she said.
>>> s = 'First line.\nSecond line.' # \n means newline
>>> s # without print(), \n is included in the output
'First line.\nSecond line.'
>>> print(s) # with print(), \n produces a new line
First line.
Second line.
hello = "This is a rather long string containing\n\ If you don't want characters prefaced by ``\`` to be interpreted as
several lines of text just as you would do in C.\n\ special characters, you can use *raw strings* by adding an ``r`` before
Note that whitespace at the beginning of the line is\ the first quote::
significant."
print(hello) >>> print('C:\some\name') # here \n means newline!
C:\some
ame
>>> print(r'C:\some\name') # note the r before the quote
C:\some\name
Note that newlines still need to be embedded in the string using ``\n`` -- the String literals can span multiple lines. One way is using triple-quotes:
newline following the trailing backslash is discarded. This example would print ``"""..."""`` or ``'''...'''``. End of lines are automatically
the following: included in the string, but it's possible to prevent this by adding a ``\`` at
the end of the line. The following example::
.. code-block:: text
This is a rather long string containing
several lines of text just as you would do in C.
Note that whitespace at the beginning of the line is significant.
Or, strings can be surrounded in a pair of matching triple-quotes: ``"""`` or
``'''``. End of lines do not need to be escaped when using triple-quotes, but
they will be included in the string. So the following uses one escape to
avoid an unwanted initial blank line. ::
print("""\ print("""\
Usage: thingy [OPTIONS] Usage: thingy [OPTIONS]
@ -228,7 +193,7 @@ avoid an unwanted initial blank line. ::
-H hostname Hostname to connect to -H hostname Hostname to connect to
""") """)
produces the following output: produces the following output (note that the initial newline is not included):
.. code-block:: text .. code-block:: text
@ -236,143 +201,100 @@ produces the following output:
-h Display this usage message -h Display this usage message
-H hostname Hostname to connect to -H hostname Hostname to connect to
If we make the string literal a "raw" string, ``\n`` sequences are not converted
to newlines, but the backslash at the end of the line, and the newline character
in the source, are both included in the string as data. Thus, the example::
hello = r"This is a rather long string containing\n\
several lines of text much as you would do in C."
print(hello)
would print:
.. code-block:: text
This is a rather long string containing\n\
several lines of text much as you would do in C.
Strings can be concatenated (glued together) with the ``+`` operator, and Strings can be concatenated (glued together) with the ``+`` operator, and
repeated with ``*``:: repeated with ``*``::
>>> word = 'Help' + 'A' >>> # 3 times 'un', followed by 'ium'
>>> word >>> 3 * 'un' + 'ium'
'HelpA' 'unununium'
>>> '<' + word*5 + '>'
'<HelpAHelpAHelpAHelpAHelpA>'
Two string literals next to each other are automatically concatenated; the first Two or more *string literals* (i.e. the ones enclosed between quotes) next
line above could also have been written ``word = 'Help' 'A'``; this only works to each other are automatically concatenated. ::
with two literals, not with arbitrary string expressions::
>>> 'str' 'ing' # <- This is ok >>> 'Py' 'thon'
'string' 'Python'
>>> 'str'.strip() + 'ing' # <- This is ok
'string' This only works with two literals though, not with variables or expressions::
>>> 'str'.strip() 'ing' # <- This is invalid
File "<stdin>", line 1, in ? >>> prefix = 'Py'
'str'.strip() 'ing' >>> prefix 'thon' # can't concatenate a variable and a string literal
^ ...
SyntaxError: invalid syntax
>>> ('un' * 3) 'ium'
...
SyntaxError: invalid syntax SyntaxError: invalid syntax
Strings can be subscripted (indexed); like in C, the first character of a string If you want to concatenate variables or a variable and a literal, use ``+``::
has subscript (index) 0. There is no separate character type; a character is
simply a string of size one. As in the Icon programming language, substrings
can be specified with the *slice notation*: two indices separated by a colon.
::
>>> word[4] >>> prefix + 'thon'
'A' 'Python'
>>> word[0:2]
'He' This feature is particularly useful when you want to break long strings::
>>> word[2:4]
'lp' >>> text = ('Put several strings within parentheses '
'to have them joined together.')
>>> text
'Put several strings within parentheses to have them joined together.'
Strings can be *indexed* (subscripted), with the first character having index 0.
There is no separate character type; a character is simply a string of size
one::
>>> word = 'Python'
>>> word[0] # character in position 0
'P'
>>> word[5] # character in position 5
'n'
Indices may also be negative numbers, to start counting from the right::
>>> word[-1] # last character
'n'
>>> word[-2] # second-last character
'o'
>>> word[-6]
'P'
Note that since -0 is the same as 0, negative indices start from -1.
In addition to indexing, *slicing* is also supported. While indexing is used
to obtain individual characters, *slicing* allows you to obtain substring::
>>> word[0:2] # characters from position 0 (included) to 2 (excluded)
'Py'
>>> word[2:5] # characters from position 2 (included) to 4 (excluded)
'tho'
Note how the start is always included, and the end always excluded. This
makes sure that ``s[:i] + s[i:]`` is always equal to ``s``::
>>> word[:2] + word[2:]
'Python'
>>> word[:4] + word[4:]
'Python'
Slice indices have useful defaults; an omitted first index defaults to zero, an Slice indices have useful defaults; an omitted first index defaults to zero, an
omitted second index defaults to the size of the string being sliced. :: omitted second index defaults to the size of the string being sliced. ::
>>> word[:2] # The first two characters >>> word[:2] # character from the beginning to position 2 (excluded)
'He' 'Py'
>>> word[2:] # Everything except the first two characters >>> word[4:] # characters from position 4 (included) to the end
'lpA' 'on'
>>> word[-2:] # characters from the second-last (included) to the end
Unlike a C string, Python strings cannot be changed. Assigning to an indexed 'on'
position in the string results in an error::
>>> word[0] = 'x'
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'str' object does not support item assignment
>>> word[:1] = 'Splat'
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: 'str' object does not support slice assignment
However, creating a new string with the combined content is easy and efficient::
>>> 'x' + word[1:]
'xelpA'
>>> 'Splat' + word[4]
'SplatA'
Here's a useful invariant of slice operations: ``s[:i] + s[i:]`` equals ``s``.
::
>>> word[:2] + word[2:]
'HelpA'
>>> word[:3] + word[3:]
'HelpA'
Degenerate slice indices are handled gracefully: an index that is too large is
replaced by the string size, an upper bound smaller than the lower bound returns
an empty string. ::
>>> word[1:100]
'elpA'
>>> word[10:]
''
>>> word[2:1]
''
Indices may be negative numbers, to start counting from the right. For example::
>>> word[-1] # The last character
'A'
>>> word[-2] # The last-but-one character
'p'
>>> word[-2:] # The last two characters
'pA'
>>> word[:-2] # Everything except the last two characters
'Hel'
But note that -0 is really the same as 0, so it does not count from the right!
::
>>> word[-0] # (since -0 equals 0)
'H'
Out-of-range negative slice indices are truncated, but don't try this for
single-element (non-slice) indices::
>>> word[-100:]
'HelpA'
>>> word[-10] # error
Traceback (most recent call last):
File "<stdin>", line 1, in ?
IndexError: string index out of range
One way to remember how slices work is to think of the indices as pointing One way to remember how slices work is to think of the indices as pointing
*between* characters, with the left edge of the first character numbered 0. *between* characters, with the left edge of the first character numbered 0.
Then the right edge of the last character of a string of *n* characters has Then the right edge of the last character of a string of *n* characters has
index *n*, for example:: index *n*, for example::
+---+---+---+---+---+ +---+---+---+---+---+---+
| H | e | l | p | A | | P | y | t | h | o | n |
+---+---+---+---+---+ +---+---+---+---+---+---+
0 1 2 3 4 5 0 1 2 3 4 5 6
-5 -4 -3 -2 -1 -6 -5 -4 -3 -2 -1
The first row of numbers gives the position of the indices 0...5 in the string; The first row of numbers gives the position of the indices 0...6 in the string;
the second row gives the corresponding negative indices. The slice from *i* to the second row gives the corresponding negative indices. The slice from *i* to
*j* consists of all characters between the edges labeled *i* and *j*, *j* consists of all characters between the edges labeled *i* and *j*,
respectively. respectively.
@ -381,6 +303,38 @@ For non-negative indices, the length of a slice is the difference of the
indices, if both are within bounds. For example, the length of ``word[1:3]`` is indices, if both are within bounds. For example, the length of ``word[1:3]`` is
2. 2.
Attempting to use a index that is too large will result in an error::
>>> word[42] # the word only has 7 characters
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IndexError: string index out of range
However, out of range slice indexes are handled gracefully when used for
slicing::
>>> word[4:42]
'on'
>>> word[42:]
''
Python strings cannot be changed --- they are :term:`immutable`.
Therefore, assigning to an indexed position in the string results in an error::
>>> word[0] = 'J'
...
TypeError: 'str' object does not support item assignment
>>> word[2:] = 'py'
...
TypeError: 'str' object does not support item assignment
If you need a different string, you should create a new one::
>>> 'J' + word[1:]
'Jython'
>>> word[:2] + 'py'
'Pypy'
The built-in function :func:`len` returns the length of a string:: The built-in function :func:`len` returns the length of a string::
>>> s = 'supercalifragilisticexpialidocious' >>> s = 'supercalifragilisticexpialidocious'
@ -407,51 +361,6 @@ The built-in function :func:`len` returns the length of a string::
the left operand of the ``%`` operator are described in more detail here. the left operand of the ``%`` operator are described in more detail here.
.. _tut-unicodestrings:
About Unicode
-------------
.. sectionauthor:: Marc-André Lemburg <mal@lemburg.com>
Starting with Python 3.0 all strings support Unicode (see
http://www.unicode.org/).
Unicode has the advantage of providing one ordinal for every character in every
script used in modern and ancient texts. Previously, there were only 256
possible ordinals for script characters. Texts were typically bound to a code
page which mapped the ordinals to script characters. This lead to very much
confusion especially with respect to internationalization (usually written as
``i18n`` --- ``'i'`` + 18 characters + ``'n'``) of software. Unicode solves
these problems by defining one code page for all scripts.
If you want to include special characters in a string,
you can do so by using the Python *Unicode-Escape* encoding. The following
example shows how::
>>> 'Hello\u0020World !'
'Hello World !'
The escape sequence ``\u0020`` indicates to insert the Unicode character with
the ordinal value 0x0020 (the space character) at the given position.
Other characters are interpreted by using their respective ordinal values
directly as Unicode ordinals. If you have literal strings in the standard
Latin-1 encoding that is used in many Western countries, you will find it
convenient that the lower 256 characters of Unicode are the same as the 256
characters of Latin-1.
Apart from these standard encodings, Python provides a whole set of other ways
of creating Unicode strings on the basis of a known encoding.
To convert a string into a sequence of bytes using a specific encoding,
string objects provide an :func:`encode` method that takes one argument, the
name of the encoding. Lowercase names for encodings are preferred. ::
>>> "Äpfel".encode('utf-8')
b'\xc3\x84pfel'
.. _tut-lists: .. _tut-lists:
Lists Lists
@ -459,97 +368,89 @@ Lists
Python knows a number of *compound* data types, used to group together other Python knows a number of *compound* data types, used to group together other
values. The most versatile is the *list*, which can be written as a list of values. The most versatile is the *list*, which can be written as a list of
comma-separated values (items) between square brackets. List items need not all comma-separated values (items) between square brackets. Lists might contain
have the same type. :: items of different types, but usually the items all have the same type. ::
>>> a = ['spam', 'eggs', 100, 1234] >>> squares = [1, 2, 4, 9, 16, 25]
>>> a >>> squares
['spam', 'eggs', 100, 1234] [1, 2, 4, 9, 16, 25]
Like string indices, list indices start at 0, and lists can be sliced, Like strings (and all other built-in :term:`sequence` type), lists can be
concatenated and so on:: indexed and sliced::
>>> a[0] >>> squares[0] # indexing returns the item
'spam' 1
>>> a[3] >>> squares[-1]
1234 25
>>> a[-2] >>> squares[-3:] # slicing returns a new list
100 [9, 16, 25]
>>> a[1:-1]
['eggs', 100]
>>> a[:2] + ['bacon', 2*2]
['spam', 'eggs', 'bacon', 4]
>>> 3*a[:3] + ['Boo!']
['spam', 'eggs', 100, 'spam', 'eggs', 100, 'spam', 'eggs', 100, 'Boo!']
All slice operations return a new list containing the requested elements. This All slice operations return a new list containing the requested elements. This
means that the following slice returns a shallow copy of the list *a*:: means that the following slice returns a new (shallow) copy of the list::
>>> a[:] >>> squares[:]
['spam', 'eggs', 100, 1234] [1, 2, 4, 9, 16, 25]
Unlike strings, which are *immutable*, it is possible to change individual Lists also supports operations like concatenation::
elements of a list::
>>> a >>> squares + [36, 49, 64, 81, 100]
['spam', 'eggs', 100, 1234] [1, 2, 4, 9, 16, 25, 36, 49, 64, 81, 100]
>>> a[2] = a[2] + 23
>>> a Unlike strings, which are :term:`immutable`, lists are a :term:`mutable`
['spam', 'eggs', 123, 1234] type, i.e. it is possible to change their content::
>>> cubes = [1, 8, 27, 65, 125] # something's wrong here
>>> 4 ** 3 # the cube of 4 is 64, not 65!
64
>>> cubes[3] = 64 # replace the wrong value
>>> cubes
[1, 8, 27, 64, 125]
You can also add new items at the end of the list, by using
the :meth:`~list.append` *method* (we will see more about methods later)::
>>> cubes.append(216) # add the cube of 6
>>> cubes.append(7 ** 3) # and the cube of 7
>>> cubes
[1, 8, 27, 64, 125, 216, 343]
Assignment to slices is also possible, and this can even change the size of the Assignment to slices is also possible, and this can even change the size of the
list or clear it entirely:: list or clear it entirely::
>>> # Replace some items: >>> letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g']
... a[0:2] = [1, 12] >>> letters
>>> a ['a', 'b', 'c', 'd', 'e', 'f', 'g']
[1, 12, 123, 1234] >>> # replace some values
>>> # Remove some: >>> letters[2:5] = ['C', 'D', 'E']
... a[0:2] = [] >>> letters
>>> a ['a', 'b', 'C', 'D', 'E', 'f', 'g']
[123, 1234] >>> # now remove them
>>> # Insert some: >>> letters[2:5] = []
... a[1:1] = ['bletch', 'xyzzy'] >>> letters
>>> a ['a', 'b', 'f', 'g']
[123, 'bletch', 'xyzzy', 1234] >>> # clear the list by replacing all the elements with an empty list
>>> # Insert (a copy of) itself at the beginning >>> letters[:] = []
>>> a[:0] = a >>> letters
>>> a
[123, 'bletch', 'xyzzy', 1234, 123, 'bletch', 'xyzzy', 1234]
>>> # Clear the list: replace all items with an empty list
>>> a[:] = []
>>> a
[] []
The built-in function :func:`len` also applies to lists:: The built-in function :func:`len` also applies to lists::
>>> a = ['a', 'b', 'c', 'd'] >>> letters = ['a', 'b', 'c', 'd']
>>> len(a) >>> len(letters)
4 4
It is possible to nest lists (create lists containing other lists), for It is possible to nest lists (create lists containing other lists), for
example:: example::
>>> q = [2, 3] >>> a = ['a', 'b', 'c']
>>> p = [1, q, 4] >>> n = [1, 2, 3]
>>> len(p) >>> x = [a, n]
3 >>> x
>>> p[1] [['a', 'b', 'c'], [1, 2, 3]]
[2, 3] >>> p[0]
>>> p[1][0] ['a', 'b', 'c']
2 >>> p[0][1]
'b'
You can add something to the end of the list::
>>> p[1].append('xtra')
>>> p
[1, [2, 3, 'xtra'], 4]
>>> q
[2, 3, 'xtra']
Note that in the last example, ``p[1]`` and ``q`` really refer to the same
object! We'll come back to *object semantics* later.
.. _tut-firststeps: .. _tut-firststeps:
@ -620,3 +521,15 @@ This example introduces several new features.
... a, b = b, a+b ... a, b = b, a+b
... ...
1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987, 1,1,2,3,5,8,13,21,34,55,89,144,233,377,610,987,
.. rubric:: Footnotes
.. [#] Since ``**`` has higher precedence than ``-``, ``-3**2`` will be
interpreted as ``-(3**2)`` and thus result in ``-9``. To avoid this
and get ``9``, you can use ``(-3)**2``.
.. [#] Unlike other languages, special characters such as ``\n`` have the
same meaning with both single (``'...'``) and double (``"..."``) quotes.
The only difference between the two is that within single quotes you don't
need to escape ``"`` (but you have to escape ``\'``) and vice versa.

2
Misc/NEWS
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@ -323,6 +323,8 @@ Tests
Documentation Documentation
------------- -------------
- Issue #14097: improve the "introduction" page of the tutorial.
- Issue #17977: The documentation for the cadefault argument's default value - Issue #17977: The documentation for the cadefault argument's default value
in urllib.request.urlopen() is fixed to match the code. in urllib.request.urlopen() is fixed to match the code.