Incorrect "unsupported-membership-test" error on subprocess.check_output

[ncoghlan]

(Migrating from pylint-dev/pylint#3045 (comment))

Steps to reproduce

1. Perform a substring check on the result of subprocess.check_output

Current behavior

pylint reports E1135 (unsupported-membership-test)

Expected behavior

pylint allows the operation (since both bytes and strings support containment checks, and those are the two possible return types from check_output)

Software version

The error was found on Debian 9 with pylint 2.3.1, astroid 2.2.5, and Python 3.5.3.

Additional info

import subprocess

bytes_data = subprocess.check_output(['echo', 'hello']);
text_data = subprocess.check_output(['echo', 'hello'], universal_newlines=True);

print(b'bytes' in bytes_data) # Prints False
print('text' in text_data)    # Prints False
'text' in bytes_data   # Runtime TypeError
b'bytes' in text_data  # Runtime TypeError

$ pylint -E check_pylint_e1135.py
************* Module check_pylint_e1135
check_pylint_e1135.py:6:18: E1135: Value 'bytes_data' doesn't support membership test (unsupported-membership-test)
check_pylint_e1135.py:7:16: E1135: Value 'text_data' doesn't support membership test (unsupported-membership-test)
check_pylint_e1135.py:8:10: E1135: Value 'bytes_data' doesn't support membership test (unsupported-membership-test)
check_pylint_e1135.py:9:12: E1135: Value 'text_data' doesn't support membership test (unsupported-membership-test)

[ncoghlan]

Thank you!