third_party/pycoverage/coverage/fullcoverage/encodings.py

   1 """Imposter encodings module that installs a coverage-style tracer.
   2
   3 This is NOT the encodings module; it is an imposter that sets up tracing
   4 instrumentation and then replaces itself with the real encodings module.
   5
   6 If the directory that holds this file is placed first in the PYTHONPATH when
   7 using "coverage" to run Python's tests, then this file will become the very
   8 first module imported by the internals of Python 3.  It installs a
   9 coverage-compatible trace function that can watch Standard Library modules
  10 execute from the very earliest stages of Python's own boot process.  This fixes
  11 a problem with coverage - that it starts too late to trace the coverage of many
  12 of the most fundamental modules in the Standard Library.
  13
  14 """
  15
  16 import sys
  17
  18 class FullCoverageTracer(object):
  19     def __init__(self):
  20         # `traces` is a list of trace events.  Frames are tricky: the same
  21         # frame object is used for a whole scope, with new line numbers
  22         # written into it.  So in one scope, all the frame objects are the
  23         # same object, and will eventually all will point to the last line
  24         # executed.  So we keep the line numbers alongside the frames.
  25         # The list looks like:
  26         #
  27         #   traces = [
  28         #       ((frame, event, arg), lineno), ...
  29         #       ]
  30         #
  31         self.traces = []
  32
  33     def fullcoverage_trace(self, *args):
  34         frame, event, arg = args
  35         self.traces.append((args, frame.f_lineno))
  36         return self.fullcoverage_trace
  37
  38 sys.settrace(FullCoverageTracer().fullcoverage_trace)
  39
  40 # In coverage/files.py is actual_filename(), which uses glob.glob.  I don't
  41 # understand why, but that use of glob borks everything if fullcoverage is in
  42 # effect.  So here we make an ugly hail-mary pass to switch off glob.glob over
  43 # there.  This means when using fullcoverage, Windows path names will not be
  44 # their actual case.
  45
  46 #sys.fullcoverage = True
  47
  48 # Finally, remove our own directory from sys.path; remove ourselves from
  49 # sys.modules; and re-import "encodings", which will be the real package
  50 # this time.  Note that the delete from sys.modules dictionary has to
  51 # happen last, since all of the symbols in this module will become None
  52 # at that exact moment, including "sys".
  53
  54 parentdir = max(filter(__file__.startswith, sys.path), key=len)
  55 sys.path.remove(parentdir)
  56 del sys.modules['encodings']
  57 import encodings