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@lonetwin
Created Apr 14, 2018
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tracer.py - Quick and dirty python 'strace'
#!/usr/bin/python
""" tracer.py: Quick and dirty python 'strace'
"""
import os
import os.path
import sys
import linecache
from functools import wraps
class tracer(object):
"""
Let's say you want to trace a function/method ``foo``::
...
...
def foo(args):
<stuff you are interested in>
...
...
You simply add the following::
from tracer import tracer
...
...
@tracer
def foo(args):
<stuff you are interested in>
...
...
Now, your function is setup for tracing. Note however, by default nothing
will be traced and the tracer() function will effectively be a noop until
there is a DEBUG variable set in the processes environment at runtime.
So, assuming that the function/method ``foo`` is called when the command
``fancyapp`` is run::
$ fancyapp # will *not* enable tracing
$ DEBUG=1 fancyapp # will enable tracing
caveats:
* this tool skips over system modules (ie: anything under
<sys.prefix>/lib/ ) and builtins. This behavior can be changed by
overriding the is_ignored() method.
* this tool currently spits its output to stderr, it might be better to
send output to a log file instead.
"""
def __init__(self, fn):
self.indent = ''
self.fn = fn
def is_ignored(self, filename):
""" is_ignored(filename) -> True or False
Are calls within this filename skipped during a trace ?
"""
system_path = os.path.dirname( sys.modules['os'].__file__ )
return True if ( # skip over
filename.startswith(system_path) or # - system modules
filename.startswith('<') or # - builtins like <string>
__file__.find(filename) != -1 # - /this/ module
) else False
def trace_fn(self, frame, event, arg):
""" trace_fn(frame, event, arg) -> trace_fn
The tracing function that'll be set using the ``sys.settrace()`` call.
"""
filename = frame.f_code.co_filename
if self.is_ignored(filename):
return self.trace_fn
lineno = frame.f_lineno
src = linecache.getline(filename, lineno).strip()
filename = filename if len(filename) < 30 else '...' + filename[-27:]
if event in ('call', 'return'):
fn = frame.f_code.co_name
if event == 'call':
args = ''
if frame.f_code.co_argcount > 0:
args = ', '.join('%s = %s' % (k, repr(v)) for k, v in frame.f_locals.items())
sys.stderr.write("%30s +%-5s |%s%s(%s)\n" % (filename, lineno, self.indent, fn, args))
self.indent += ' '
else:
self.indent = self.indent[:-2]
if src.find('return') != -1:
sys.stderr.write("%30s +%-5s |%s%s <= %s\n" % (filename, lineno, self.indent, fn, src.replace('return', '')))
else:
sys.stderr.write("%30s +%-5s |%s%s() <= None\n" % (filename, lineno, self.indent, fn))
else:
sys.stderr.write("%30s +%-5s |%s%s\n" % (filename, lineno, self.indent, src))
return self.trace_fn
def __call__(self, *args, **kwargs):
if os.environ.get('DEBUG', None):
@wraps(self.fn)
def traceit(*args, **kwargs):
tracer = sys.gettrace()
try:
sys.settrace(self.trace_fn)
return self.fn(*args, **kwargs)
finally:
sys.settrace(tracer)
return traceit(*args, **kwargs)
else:
return self.fn(*args, **kwargs)
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