CODEWITHSUNDEEP
python
Stefan Vonk
Stefan Vonk

Reputation: 25

External library uses print instead of return

I have a problem with an external library that I use in my script.

I execute a function from this library, but the function prints the output directly. However, I need the output to check if there is a specific string in it.

How can I ensure that the output of the function in the external library comes in a variable so that I can make the comparisons with the string?

Upvotes: 1

Views: 211

Answers (2)

Lin GU
Lin GU

Reputation: 89

You can exchange sys.stdout with your buffer temporarily, and then check the buffer.

def external_method():
  print ("print something out, don't return")

class MyBuffer(object):
  def __init__(self):
    self.buffer = []
  def write(self, *args, **kwargs):
    self.buffer.append(args)

import sys
old_stdout = sys.stdout
sys.stdout = MyBuffer()
external_method()
my_buffer, sys.stdout = sys.stdout, old_stdout
print (my_buffer.buffer)

Upvotes: 1

Eric Duminil
Eric Duminil

Reputation: 54263

If you really have no other choice, you could redirect stdout when you call the library. Here's a piece of code adapted from this answer :

def some_library():
    print("Should probably return instead of print.")

import sys
from io import StringIO

class redirected_stdout:
    def __init__(self):
        self._stdout = None
        self._string_io = None

    def __enter__(self):
        self._stdout = sys.stdout
        sys.stdout = self._string_io = StringIO()
        return self

    def __exit__(self, type, value, traceback):
        sys.stdout = self._stdout

    @property
    def string(self):
        return self._string_io.getvalue()

with redirected_stdout() as out:
    some_library()
    result = out.string

print("return" in result)
# True

It would be much cleaner to modify the library, though.

Upvotes: 2

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