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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 # Finally, remove our own directory from sys.path; remove ourselves from | |
41 # sys.modules; and re-import "encodings", which will be the real package | |
42 # this time. Note that the delete from sys.modules dictionary has to | |
43 # happen last, since all of the symbols in this module will become None | |
44 # at that exact moment, including "sys". | |
45 | |
46 parentdirs = [ d for d in sys.path if __file__.startswith(d) ] | |
47 parentdirs.sort(key=len) | |
48 sys.path.remove(parentdirs[-1]) | |
49 del sys.modules['encodings'] | |
50 import encodings | |
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