Richard Wolff's changes:
pdb.doc Updated to reflect better the various changes.
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Guido van Rossum
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Lib/pdb.doc
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Lib/pdb.doc
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The Python Debugger
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===================
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The Python Debugger Pdb
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=======================
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To use the debugger in its simplest form:
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>>> import pdb
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>>> pdb.run('<a statement>')
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>>> import pdb
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>>> pdb.run('<a statement>')
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The debugger's prompt is '(Pdb) '. This will stop in the first
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function call in <a statement>.
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@ -13,10 +13,10 @@ Alternatively, if a statement terminated with an unhandled exception,
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you can use pdb's post-mortem facility to inspect the contents of the
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traceback:
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>>> <a statement>
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<exception traceback>
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>>> import pdb
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>>> pdb.pm()
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>>> <a statement>
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<exception traceback>
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>>> import pdb
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>>> pdb.pm()
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The commands recognized by the debugger are listed in the next
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section. Most can be abbreviated as indicated; e.g., h(elp) means
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@ -24,8 +24,8 @@ that 'help' can be typed as 'h' or 'help' (but not as 'he' or 'hel',
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nor as 'H' or 'Help' or 'HELP'). Optional arguments are enclosed in
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square brackets.
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A blank line repeats the previous command literally. (Except for
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'list', where it lists the next 11 lines.)
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A blank line repeats the previous command literally, except for
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'list', where it lists the next 11 lines.
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Commands that the debugger doesn't recognize are assumed to be Python
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statements and are executed in the context of the program being
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@ -35,90 +35,208 @@ debugged; it is even possible to change variables. When an exception
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occurs in such a statement, the exception name is printed but the
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debugger's state is not changed.
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The debugger is not directly programmable; but it is implemented as a
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class from which you can derive your own debugger class, so you can
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make as fancy as you like.
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The debugger supports aliases, which can save typing. And aliases
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can have parameters (see the alias help entry) which allows one a
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certain level of adaptability to the context under examination.
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Multiple commands may be entered on a single line, separated by
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semi-colons. No intelligence is applied to separating the commands;
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the input is split at the first ';', even if it is in the middle of
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a quoted string.
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If a file ".pdbrc" exists in your home directory or in the current
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directory, it is read in and executed as if it had been typed at
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the debugger prompt. This is particularly useful for aliases.
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If both files exist, the one in the home directory is read first
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and aliases defined there can be overriden by the local file.
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Aside from aliases, the debugger is not directly programmable; but
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it is implemented as a class from which you can derive your own
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debugger class, which you can make as fancy as you like.
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Debugger commands
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=================
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h(elp)
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Without argument, print the list of available commands.
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With a command name as argument, print help about that command
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"help pdb" pipes the full documentation file to the $PAGER
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"help exec" gives help on the ! command
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Without argument, print the list of available commands.
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With a command name as argument, print help about that command
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(this is currently not implemented).
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w(here)
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Print a stack trace, with the most recent frame at the bottom.
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An arrow indicates the "current frame", which determines the
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context of most commands.
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Print a stack trace, with the most recent frame at the bottom.
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An arrow indicates the "current frame", which determines the
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context of most commands.
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d(own)
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Move the current frame one level down in the stack trace
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(to an older frame).
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Move the current frame one level down in the stack trace
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(to an older frame).
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u(p)
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Move the current frame one level up in the stack trace
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(to a newer frame).
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Move the current frame one level up in the stack trace
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(to a newer frame).
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b(reak) ([file:]lineno | function) [, "condition"]
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With a line number argument, set a break there in the current
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file. With a function name, set a break at the entry of that
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function. Without argument, list all breaks. If a second
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argument is present, it is a string specifying an expression
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which must evaluate to true before the breakpoint is honored.
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b(reak) [ ([filename:]lineno | function) [, "condition"] ]
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With a filename:line number argument, set a break there. If
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filename is omitted, use the current file. With a function name,
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set a break at the first executable line of that function.
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Without argument, list all breaks. Each breakpoint is assigned
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a number which is by all the other breakpoint commands refer to it.
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The line number may be prefixed with a filename and a colon,
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to specify a breakpoint in another file (probably one that
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hasn't been loaded yet). The file is searched on sys.path.
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The condition argument, if present, is a string which must
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evaluate to true in order for the breakpoint to be honored.
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cl(ear) [lineno]
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With a line number argument, clear that break in the current file.
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Without argument, clear all breaks (but first ask confirmation).
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tbreak [ ([filename:]lineno | function) [, "condition"] ]
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Temporary breakpoint, which is removed automatically when it is
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first hit. The arguments are the same as break.
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The line number may be prefixed with a filename and a colon,
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to specify a breakpoint in another file (probably one that
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hasn't been loaded yet). The file is searched on sys.path.
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cl(ear) [bpnumber [bpnumber ...] ]
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With a space separated list of breakpoint numbers, clear those
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breakpoints. Without argument, clear all breaks (but first
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ask confirmation).
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disable bpnumber [bpnumber ...]
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Disables the breakpoints given as a space separated list of
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breakpoint numbers. Disabling a breakpoint means it cannot cause
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the program to stop execution, but unlike clearing a breakpoint, it
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remains in the list of breakpoints and can be (re-)enabled.
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enable bpnumber [bpnumber ...]
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Enables the breakpoints specified.
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ignore bpnumber count
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Sets the ignore count for the given breakpoint number. If
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count is omitted, the ignore count is set to 0. A breakpoint
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becomes active when the ignore count is zero. When non-zero,
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the count is decremented each time the breakpoint is reached
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and the breakpoint is not disabled and any associated condition
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evaluates to true.
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condition bpnumber str_condition
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str_condition is a string specifying an expression which
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must evaluate to true before the breakpoint is honored.
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If str_condition is absent, any existing condition is removed;
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i.e., the breakpoint is made unconditional.
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s(tep)
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Execute the current line, stop at the first possible occasion
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(either in a function that is called or in the current function).
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Execute the current line, stop at the first possible occasion
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(either in a function that is called or in the current function).
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n(ext)
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Continue execution until the next line in the current function
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is reached or it returns.
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Continue execution until the next line in the current function
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is reached or it returns.
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r(eturn)
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Continue execution until the current function returns.
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Continue execution until the current function returns.
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c(ont(inue))
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Continue execution, only stop when a breakpoint is encountered.
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Continue execution, only stop when a breakpoint is encountered.
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l(ist) [first [,last]]
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List source code for the current file.
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Without arguments, list 11 lines around the current line
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or continue the previous listing.
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With one argument, list 11 lines starting at that line.
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With two arguments, list the given range;
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if the second argument is less than the first, it is a count.
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List source code for the current file.
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Without arguments, list 11 lines around the current line
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or continue the previous listing.
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With one argument, list 11 lines starting at that line.
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With two arguments, list the given range;
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if the second argument is less than the first, it is a count.
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a(rgs)
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Print the argument list of the current function.
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Print the argument list of the current function.
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p expression
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Print the value of the expression.
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Print the value of the expression.
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(!) statement
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Execute the (one-line) statement in the context of
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the current stack frame.
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The exclamation point can be omitted unless the first word
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of the statement resembles a debugger command.
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To assign to a global variable you must always prefix the
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command with a 'global' command, e.g.:
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(Pdb) global list_options; list_options = ['-l']
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(Pdb)
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Execute the (one-line) statement in the context of the current
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stack frame. The exclamation point can be omitted unless the
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first word of the statement resembles a debugger command.
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To assign to a global variable you must always prefix the
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command with a 'global' command, e.g.:
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(Pdb) global list_options; list_options = ['-l']
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(Pdb)
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whatis arg
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Prints the type of the argument.
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alias [name [command]]
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Creates an alias called 'name' that executes 'command'. The command
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must *not* be enclosed in quotes. Replaceable parameters can be
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indicated by %1, %2, and so on, while %* is replaced by all the
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parameters. If no command is given, the current alias for name
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is shown. If no name is given, all aliases are listed.
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Aliases may be nested and can contain anything that can be
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legally typed at the pdb prompt. Note! You *can* override
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internal pdb commands with aliases! Those internal commands
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are then hidden until the alias is removed. Aliasing is recursively
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applied to the first word of the command line; all other words
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in the line are left alone.
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As an example, here are two useful aliases (especially when placed
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in the .pdbrc file):
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#Print instance variables (usage "pi classInst")
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alias pi for k in %1.__dict__.keys(): print "%1." + k + "=" + %1.__dict__[k]
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#Print instance variables in self
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alias ps pi self
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unalias name
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Deletes the specified alias.
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q(uit)
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Quit from the debugger.
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The program being executed is aborted.
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Quit from the debugger.
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The program being executed is aborted.
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How it works
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============
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Some changes were made to the interpreter:
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- sys.settrace(func) sets the global trace function
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- there can also a local trace function (see later)
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Trace functions have three arguments: (frame, event, arg)
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- frame is the current stack frame
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- event is a string: 'call', 'line', 'return' or 'exception'
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- arg is dependent on the event type
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A trace function should return a new trace function or None.
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Class methods are accepted (and most useful!) as trace methods.
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The events have the following meaning:
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'call': A function is called (or some other code block entered).
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The global trace function is called;
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arg is the argument list to the function;
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the return value specifies the local trace function.
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'line': The interpreter is about to execute a new line of code
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(sometimes multiple line events on one line exist).
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The local trace function is called; arg in None;
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the return value specifies the new local trace function.
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'return': A function (or other code block) is about to return.
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The local trace function is called;
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arg is the value that will be returned.
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The trace function's return value is ignored.
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'exception': An exception has occurred.
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The local trace function is called;
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arg is a triple (exception, value, traceback);
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the return value specifies the new local trace function
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Note that as an exception is propagated down the chain of callers, an
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'exception' event is generated at each level.
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Stack frame objects have the following read-only attributes:
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f_code: the code object being executed
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f_lineno: the current line number (-1 for 'call' events)
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f_back: the stack frame of the caller, or None
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f_locals: dictionary containing local name bindings
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f_globals: dictionary containing global name bindings
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Code objects have the following read-only attributes:
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co_code: the code string
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co_names: the list of names used by the code
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co_consts: the list of (literal) constants used by the code
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co_filename: the filename from which the code was compiled
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