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Commit 6fe08b0f authored by Guido van Rossum's avatar Guido van Rossum
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Moved documentation out to pdb.doc file. 

Moved class Cmd out to module cmd.py.
Rewrote implementation of stack trace to incorporate traceback objects.
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Lib/pdb.py
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# pdb.py -- finally, a Python debugger! See below for instructions.
# pdb.py -- finally, a Python debugger!
# See file pdb.doc for instructions.
# To do:
# - Keep a list of exceptions trapped (default only KeyboardInterrupt?)
# - It should be possible to intercept KeyboardInterrupt completely
# - Handle return events differently (how?)
# - When stopping on an exception, show traceback stack
# - Merge with tb (for post-mortem usage)
# - Show stack traces upside-down (like dbx/gdb) ???
# (actually, the current way is more natural given the directions
# taken by the up/down commands)
# To use the debugger in its simplest form:
# >>> import pdb
# >>> pdb.run('<a statement>')
# The debugger's prompt is '(Pdb) '.
# This will stop in the first function call in <a statement>.
# The commands recognized by the debugger are listed below.
# Most can be abbreviated as indicated; e.g., h(elp) means that
# 'help' can be typed as 'h' or 'help'
# (but not as 'he' or 'hel', nor as 'H' or 'Help' or 'HELP').
# Optional arguments are enclosed in square brackets.
# A blank line repeats the previous command literally.
# (Except for 'list', where it lists the next 11 lines.)
# Commands that the debugger does not recognized are assumed to
# be Python statements and are executed in the context of the
# program being debugged.
# Python statements can also be prefixed with an exclamation point ('!').
# This is a powerful way to inspect the program being debugged;
# it is even possible to change variables.
# When an exception occurs in such a statement, the exception name
# is printed but the debugger's state is not changed.
# The debugger is not directly programmable; but it is implemented
# as a class from which you can derive your own debugger class,
# so you can make as fancy as you like.
# The debugger's commands are:
# h(elp)
# Without argument, print the list of available commands.
# With a command name as argument, print help about that command
# (this is currently not implemented).
# w(here)
# Print a stack trace, with the most recent frame at the bottom.
# An arrow indicates the "current frame", which determines the
# context of most commands.
# d(own)
# Move the current frame one level down in the stack trace
# (to an older frame).
# u(p)
# Move the current frame one level up in the stack trace
# (to a newer frame).
# b(reak) [lineno]
# With a line number argument, set a break there in the current file.
# Without argument, list all breaks.
# cl(ear) [lineno]
# With a line number argument, clear that break in the current file.
# Without argument, clear all breaks (but first ask confirmation).
# s(tep)
# Execute the current line, stop at the first possible occasion
# (either in a function that is called or in the current function).
# n(ext)
# Continue execution until the next line in the current function
# is reached or it returns.
# r(eturn)
# Continue execution until the current function returns.
# c(ont(inue))
# Continue execution, only stop when a breakpoint is encountered.
# l(ist) [first [,last]]
# List source code for the current file.
# Without arguments, list 11 lines around the current line
# or continue the previous listing.
# With one argument, list 11 lines starting at that line.
# With two arguments, list the given range;
# if the second argument is less than the first, it is a count.
# a(rgs)
# Print the argument list of the current function.
# p expression
# Print the value of the expression.
# (!) statement
# Execute the (one-line) statement in the context of
# the current stack frame.
# The exclamation point can be omitted unless the first word
# of the statement resembles a debugger command.
# To assign to a global variable you must always prefix the
# command with a 'global' command, e.g.:
# (Pdb) global list_options; list_options = ['-l']
# (Pdb)
# q(uit)
# Quit from the debugger.
# The program being executed is aborted.
# Here's how it works.
# Some changes were made to the interpreter:
# - if sys.trace is defined (by the user), it should be a function
# - sys.trace is called the global trace function
# - there can also a local trace function (see later)
# Trace functions have three arguments: (frame, event, arg)
# - frame is the current stack frame
# - event is a string: 'call', 'line', 'return' or 'exception'
# - arg is dependent on the event type
# A trace function should return a new trace function or None.
# Class methods are accepted (and most useful!) as trace methods.
# The events have the following meaning:
#
# 'call': A function is called (or some other code block entered).
# The global trace function is called;
# arg is the argument list to the function;
# the return value specifies the local trace function.
#
# 'line': The interpreter is about to execute a new line of code
# (sometimes multiple line events on one line exist).
# The local trace function is called; arg in None;
# the return value specifies the new local trace function.
#
# 'return': A function (or other code block) is about to return.
# The local trace function is called;
# arg is the value that will be returned.
# The trace function's return value is ignored.
#
# 'exception': An exception has occurred.
# The local trace function is called if there is one,
# else the global trace function is called;
# arg is a triple (exception, value, traceback);
# the return value specifies the new local trace function
#
# Note that as an exception is propagated down the chain of callers,
# an 'exception' event is generated at each level.
# A stack frame object has the following read-only attributes:
# f_code: the code object being executed
# f_lineno: the current line number (-1 for 'call' events)
# f_back: the stack frame of the caller, or None
# f_locals: dictionary containing local name bindings
# f_globals: dictionary containing global name bindings
# A code object has the following read-only attributes:
# co_code: the code string
# co_names: the list of names used by the code
# co_consts: the list of (literal) constants used by the code
# co_filename: the filename from which the code was compiled
# - It should be possible to intercept KeyboardInterrupt
# - Handle return events differently -- always printing the r.v. can be bad!
# - Merge with tb, to get a single debugger for active and post-mortem usage
# - Solve bugs in termination (e.g., 'continue' after the program
# is done proceeds to debug the debugger; 'quit' sometimes complains
# about the PdbQuit exception...)
import string
import sys
import linecache
# A generic class to build command interpreters
PROMPT = '(Cmd) '
IDENTCHARS = string.letters + string.digits + '_'
class Cmd:
def init(self):
self.prompt = PROMPT
self.identchars = IDENTCHARS
self.lastcmd = ''
return self
def cmdloop(self):
stop = None
while not stop:
try:
line = raw_input(self.prompt)
except EOFError:
line = 'EOF'
stop = self.onecmd(line)
return stop
def onecmd(self, line):
line = string.strip(line)
if not line:
line = self.lastcmd
print line
else:
self.lastcmd = line
i, n = 0, len(line)
while i < n and line[i] in self.identchars: i = i+1
cmd, arg = line[:i], string.strip(line[i:])
if cmd == '':
return self.default(line)
else:
try:
func = eval('self.do_' + cmd)
except AttributeError:
return self.default(line)
return func(arg)
def default(self, line):
print '*** Unknown syntax:', line
def do_help(self, arg):
if arg:
# XXX check arg syntax
try:
func = eval('self.help_' + arg)
except:
print '*** No help on', `arg`
return
func()
else:
import getattr
names = getattr.dir(self)
cmds = []
for name in names:
if name[:3] == 'do_':
cmds.append(name[3:])
print cmds
from cmd import Cmd
# A specialization of Cmd for use by the debugger
......@@ -242,18 +29,32 @@ class Pdb(Cmd):
return self
def reset(self):
self.quitting = 0
self.breaks = {}
self.botframe = None
self.stopframe = None
self.forget()
def forget(self):
self.setup(None)
self.setup(None, None)
def setup(self, frame):
self.curframe = self.topframe = frame
self.stack = []
def setup(self, f, t):
self.lineno = None
self.stack = []
if t and t.tb_frame is f:
t = t.tb_next
while f and f is not self.botframe:
self.stack.append((f, f.f_lineno))
f = f.f_back
self.stack.reverse()
self.curindex = max(0, len(self.stack) - 1)
while t:
self.stack.append((t.tb_frame, t.tb_lineno))
t = t.tb_next
if 0 <= self.curindex < len(self.stack):
self.curframe = self.stack[self.curindex][0]
else:
self.curframe = None
def run(self, cmd):
import __main__
......@@ -267,12 +68,21 @@ class Pdb(Cmd):
exec(cmd + '\n', globals, locals)
except PdbQuit:
pass
finally:
except:
print '***', sys.exc_type + ':', `sys.exc_value`
print '*** Post Mortem Debugging:'
sys.trace = None
del sys.trace
try:
self.ask_user(None, sys.exc_traceback)
except PdbQuit:
pass
finally:
self.reset()
def dispatch(self, frame, event, arg):
if self.quitting:
return None
if event == 'line':
return self.dispatch_line(frame)
if event == 'call':
......@@ -286,7 +96,7 @@ class Pdb(Cmd):
def dispatch_line(self, frame):
if self.stop_here(frame) or self.break_here(frame):
self.ask_user(frame)
self.ask_user(frame, None)
return self.dispatch
def dispatch_call(self, frame, arg):
......@@ -304,10 +114,9 @@ class Pdb(Cmd):
return
def dispatch_exception(self, frame, arg):
if arg[0] is PdbQuit: return None
if self.stop_here(frame):
print '!!! exception', arg[0] + ':', `arg[1]`
self.ask_user(frame)
self.ask_user(frame, arg[2])
return self.dispatch
def stop_here(self, frame):
......@@ -315,8 +124,8 @@ class Pdb(Cmd):
return 1
if frame is self.stopframe:
return 1
while frame is not self.stopframe:
if frame is None:
while frame is not None and frame is not self.stopframe:
if frame is self.botframe:
return 1
frame = frame.f_back
return 0
......@@ -332,10 +141,10 @@ class Pdb(Cmd):
def break_anywhere(self, frame):
return self.breaks.has_key(frame.f_code.co_filename)
def ask_user(self, frame):
self.setup(frame)
self.printwhere(self.curframe)
dummy = self.cmdloop()
def ask_user(self, frame, traceback):
self.setup(frame, traceback)
self.printframelineno(self.stack[self.curindex])
self.cmdloop()
self.forget()
def default(self, line):
......@@ -402,26 +211,25 @@ class Pdb(Cmd):
do_cl = do_clear # 'c' is already an abbreviation for 'continue'
def do_where(self, arg):
self.printtb()
self.printstacktrace()
do_w = do_where
def do_up(self, arg):
if self.curframe == self.botframe or \
not self.curframe.f_back: print '*** Top'
if self.curindex == 0:
print '*** Oldest frame'
else:
self.stack.append(self.curframe)
self.curframe = self.curframe.f_back
self.lineno = None
self.printwhere(self.curframe)
self.curindex = self.curindex - 1
self.curframe = self.stack[self.curindex][0]
self.printframelineno(self.stack[self.curindex])
do_u = do_up
def do_down(self, arg):
if not self.stack: print '*** Bottom'
if self.curindex + 1 == len(self.stack):
print '*** Newest frame'
else:
self.curframe = self.stack[-1]
self.lineno = None
del self.stack[-1]
self.printwhere(self.curframe)
self.curindex = self.curindex + 1
self.curframe = self.stack[self.curindex][0]
self.printframelineno(self.stack[self.curindex])
do_d = do_down
def do_step(self, arg):
......@@ -445,7 +253,8 @@ class Pdb(Cmd):
do_c = do_cont = do_continue
def do_quit(self, arg):
self.stopframe = self.botframe
self.quitting = 1
sys.trace = None; del sys.trace
raise PdbQuit
do_q = do_quit
......@@ -516,36 +325,39 @@ class Pdb(Cmd):
return
print `value`
# Print a traceback starting at a given stack frame
# Note that it is printed upside-down with respect
# to the orientation suggested by the up/down commands.
# This is consistent with gdb.
def printtb(self):
list = []
frame = self.topframe
while frame:
list.append(frame)
if frame is self.botframe: break
frame = frame.f_back
list.reverse()
for frame in list:
self.printwhere(frame)
# Print a traceback starting at the top stack frame.
# Note that the most recently entered frame is printed last;
# this is different from dbx and gdb, but consistent with
# the Python interpreter's stack trace.
# It is also consistent with the up/down commands (which are
# compatible with dbx and gdb: up moves towards 'main()'
# and down moves towards the most recent stack frame).
def printwhere(self, frame):
def printstacktrace(self):
for x in self.stack:
self.printframelineno(x)
def printframelineno(self, (frame, lineno)):
if frame is self.curframe: print '->',
code = frame.f_code
filename = code.co_filename
lineno = frame.f_lineno
print filename + '(' + `lineno` + ')',
line = linecache.getline(filename, lineno)
if line: print string.strip(line),
print string.strip(line),
print
def run(statement):
Pdb().init().run(statement)
def runctx(statement, globals, locals):
Pdb().init().runctx(statement, globals, locals)
# --------------------- testing ---------------------
# The Ackermann function -- a highly recursive beast
cheat = 0
cheat = 2
cache = {}
def ack(x, y):
key = `(long(x), long(y))`
......@@ -572,15 +384,21 @@ def foo(n):
print 'foo', n
x = bar(n*2)
print 'bar returned', x
return
y = ack(4, 3)
return y
def bar(a):
print 'bar', a
return a*10
def melt(n):
print 1.0/n
melt(n-1)
def test():
linecache.checkcache()
Pdb().init().run('foo(12)\n')
runctx('from pdb import foo; foo(12)', {}, {})
runctx('from pdb import melt; melt(5)', {}, {})
# --------------------- main ---------------------
......@@ -600,7 +418,4 @@ def main():
sys.path.insert(0, head)
run('import ' + tail[:-3])
else:
run('')
def run(statement):
Pdb().init().run(statement)
run(raw_input('Python statement to debug: '))
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