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      1 The Python Debugger Pdb
      2 =======================
      3 
      4 To use the debugger in its simplest form:
      5 
      6         >>> import pdb
      7         >>> pdb.run('<a statement>')
      8 
      9 The debugger's prompt is '(Pdb) '.  This will stop in the first
     10 function call in <a statement>.
     11 
     12 Alternatively, if a statement terminated with an unhandled exception,
     13 you can use pdb's post-mortem facility to inspect the contents of the
     14 traceback:
     15 
     16         >>> <a statement>
     17         <exception traceback>
     18         >>> import pdb
     19         >>> pdb.pm()
     20 
     21 The commands recognized by the debugger are listed in the next
     22 section.  Most can be abbreviated as indicated; e.g., h(elp) means
     23 that 'help' can be typed as 'h' or 'help' (but not as 'he' or 'hel',
     24 nor as 'H' or 'Help' or 'HELP').  Optional arguments are enclosed in
     25 square brackets.
     26 
     27 A blank line repeats the previous command literally, except for
     28 'list', where it lists the next 11 lines.
     29 
     30 Commands that the debugger doesn't recognize are assumed to be Python
     31 statements and are executed in the context of the program being
     32 debugged.  Python statements can also be prefixed with an exclamation
     33 point ('!').  This is a powerful way to inspect the program being
     34 debugged; it is even possible to change variables.  When an exception
     35 occurs in such a statement, the exception name is printed but the
     36 debugger's state is not changed.
     37 
     38 The debugger supports aliases, which can save typing.  And aliases can
     39 have parameters (see the alias help entry) which allows one a certain
     40 level of adaptability to the context under examination.
     41 
     42 Multiple commands may be entered on a single line, separated by the
     43 pair ';;'.  No intelligence is applied to separating the commands; the
     44 input is split at the first ';;', even if it is in the middle of a
     45 quoted string.
     46 
     47 If a file ".pdbrc" exists in your home directory or in the current
     48 directory, it is read in and executed as if it had been typed at the
     49 debugger prompt.  This is particularly useful for aliases.  If both
     50 files exist, the one in the home directory is read first and aliases
     51 defined there can be overriden by the local file.
     52 
     53 Aside from aliases, the debugger is not directly programmable; but it
     54 is implemented as a class from which you can derive your own debugger
     55 class, which you can make as fancy as you like.
     56 
     57 
     58 Debugger commands
     59 =================
     60 
     61 h(elp)
     62         Without argument, print the list of available commands.  With
     63         a command name as argument, print help about that command
     64         (this is currently not implemented).
     65 
     66 w(here)
     67         Print a stack trace, with the most recent frame at the bottom.
     68         An arrow indicates the "current frame", which determines the
     69         context of most commands.
     70 
     71 d(own)
     72         Move the current frame one level down in the stack trace
     73         (to a newer frame).
     74 
     75 u(p)
     76         Move the current frame one level up in the stack trace
     77         (to an older frame).
     78 
     79 b(reak) [ ([filename:]lineno | function) [, condition] ]
     80         With a filename:line number argument, set a break there.  If
     81         filename is omitted, use the current file.  With a function
     82         name, set a break at the first executable line of that
     83         function.  Without argument, list all breaks.  Each breakpoint
     84         is assigned a number to which all the other breakpoint
     85         commands refer.
     86 
     87         The condition argument, if present, is a string which must
     88         evaluate to true in order for the breakpoint to be honored.
     89 
     90 tbreak [ ([filename:]lineno | function) [, condition] ]
     91         Temporary breakpoint, which is removed automatically when it
     92         is first hit.  The arguments are the same as break.
     93 
     94 cl(ear) [bpnumber [bpnumber ...] ]
     95         With a space separated list of breakpoint numbers, clear those
     96         breakpoints.  Without argument, clear all breaks (but first
     97         ask confirmation).
     98 
     99 disable bpnumber [bpnumber ...]
    100         Disables the breakpoints given as a space separated list of
    101         breakpoint numbers.  Disabling a breakpoint means it cannot
    102         cause the program to stop execution, but unlike clearing a
    103         breakpoint, it remains in the list of breakpoints and can be
    104         (re-)enabled.
    105 
    106 enable bpnumber [bpnumber ...]
    107         Enables the breakpoints specified.
    108 
    109 ignore bpnumber count
    110         Sets the ignore count for the given breakpoint number.  If
    111         count is omitted, the ignore count is set to 0.  A breakpoint
    112         becomes active when the ignore count is zero.  When non-zero,
    113         the count is decremented each time the breakpoint is reached
    114         and the breakpoint is not disabled and any associated
    115         condition evaluates to true.
    116 
    117 condition bpnumber condition
    118         condition is an expression which must evaluate to true before
    119         the breakpoint is honored.  If condition is absent, any
    120         existing condition is removed; i.e., the breakpoint is made
    121         unconditional.
    122 
    123 s(tep)
    124         Execute the current line, stop at the first possible occasion
    125         (either in a function that is called or in the current function).
    126 
    127 n(ext)
    128         Continue execution until the next line in the current function
    129         is reached or it returns.
    130 
    131 unt(il)
    132         Continue execution until the line with a number greater than the 
    133         current one is reached or until the current frame returns.
    134 
    135 r(eturn)
    136         Continue execution until the current function returns.
    137 
    138 run [args...]
    139         Restart the debugged python program. If a string is supplied it is
    140         splitted with "shlex", and the result is used as the new sys.argv.
    141         History, breakpoints, actions and debugger options are preserved.
    142         "restart" is an alias for "run".
    143 
    144 c(ont(inue))
    145         Continue execution, only stop when a breakpoint is encountered.
    146 
    147 l(ist) [first [,last]]
    148         List source code for the current file.
    149         Without arguments, list 11 lines around the current line
    150         or continue the previous listing.
    151         With one argument, list 11 lines starting at that line.
    152         With two arguments, list the given range;
    153         if the second argument is less than the first, it is a count.
    154 
    155 a(rgs)
    156         Print the argument list of the current function.
    157 
    158 p expression
    159         Print the value of the expression.
    160 
    161 (!) statement
    162         Execute the (one-line) statement in the context of the current
    163         stack frame.  The exclamation point can be omitted unless the
    164         first word of the statement resembles a debugger command.  To
    165         assign to a global variable you must always prefix the command
    166         with a 'global' command, e.g.:
    167         (Pdb) global list_options; list_options = ['-l']
    168         (Pdb)
    169 
    170 
    171 whatis arg
    172          Prints the type of the argument.
    173 
    174 alias [name [command]]
    175         Creates an alias called 'name' that executes 'command'.  The
    176         command must *not* be enclosed in quotes.  Replaceable
    177         parameters can be indicated by %1, %2, and so on, while %* is
    178         replaced by all the parameters.  If no command is given, the
    179         current alias for name is shown. If no name is given, all
    180         aliases are listed.
    181 
    182         Aliases may be nested and can contain anything that can be
    183         legally typed at the pdb prompt.  Note!  You *can* override
    184         internal pdb commands with aliases!  Those internal commands
    185         are then hidden until the alias is removed.  Aliasing is
    186         recursively applied to the first word of the command line; all
    187         other words in the line are left alone.
    188 
    189         As an example, here are two useful aliases (especially when
    190         placed in the .pdbrc file):
    191 
    192         #Print instance variables (usage "pi classInst")
    193         alias pi for k in %1.__dict__.keys(): print "%1.",k,"=",%1.__dict__[k]
    194         #Print instance variables in self
    195         alias ps pi self
    196                 
    197 unalias name
    198         Deletes the specified alias.
    199 
    200 q(uit)
    201         Quit from the debugger.
    202         The program being executed is aborted.
    203