CODEWITHSUNDEEP
pythonpython-2.7
IT Ninja
IT Ninja

Reputation: 6438

capturing dis.dis results

Is there any way to get the output of dis.dis() without redirecting sys.stdout? I have tried:

out=str(dis.dis())

and

out=""""""
out+=str(dis.dis())

However I soon found out that it returns None. Is there any way to fix this?

Upvotes: 20

Views: 3301

Answers (2)

Rub
Rub

Reputation: 2738

If using Colab / Jupyter

In one cell you can run dis redirecting the output to a variable

%%capture dis_output
# dis : Disassembler for Python bytecode
from dis import dis
dis(function_to_check)

And then you can use it from Bash. Here an example

! echo  "{dis_output.stdout}" | grep -i global

14           4 LOAD_GLOBAL              0 (AudioLibrary)
             36 LOAD_GLOBAL              2 (userLanguageAudio)
             50 LOAD_GLOBAL              2 (userLanguageAudio)
             62 LOAD_GLOBAL              3 (LESSON_FILES_DIR)
 27          76 LOAD_GLOBAL              4 (get_ipython)
 30          96 LOAD_GLOBAL              6 (pread)
 31         104 LOAD_GLOBAL              7 (print)
 34     >>  124 LOAD_GLOBAL              7 (print)

Or from Python

print(dis_output.stdout)

Upvotes: 0

Martijn Pieters
Martijn Pieters

Reputation: 1123770

Unfortunately, in Python versions before 3.4 the dis module uses print statements to stdout, so it won't return anything directly useful. Either you have to re-implement the dis, disassemble and disassemble_string functions, or you temporarily replace sys.stdout with an alternative to capture the output:

import sys
from cStringIO import StringIO

out = StringIO()
stdout = sys.stdout
sys.stdout = out
try:
    dis.dis()
finally:
    sys.stdout = stdout
out = out.getvalue()

This is actually best done using a context manager:

import sys
from contextlib import contextmanager
from cStringIO import StringIO

@contextmanager
def captureStdOut(output):
    stdout = sys.stdout
    sys.stdout = output
    try:
        yield
    finally:
        sys.stdout = stdout

out = StringIO()
with captureStdOut(out):
    dis.dis()
print out.getvalue()

That way you are guaranteed to have stdout restored even if something goes wrong with dis. A little demonstration:

>>> out = StringIO()
>>> with captureStdOut(out):
...     dis.dis(captureStdOut)
... 
>>> print out.getvalue()
 83           0 LOAD_GLOBAL              0 (GeneratorContextManager)
              3 LOAD_DEREF               0 (func)
              6 LOAD_FAST                0 (args)
              9 LOAD_FAST                1 (kwds)
             12 CALL_FUNCTION_VAR_KW     0
             15 CALL_FUNCTION            1
             18 RETURN_VALUE

In Python 3.4 and up, the relevant functions take a file parameter to redirect output to:

from io import StringIO

with StringIO() as out:
    dis.dis(file=out)
    print(out.getvalue())

Upvotes: 29

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