I'm trying to store the output of a Function into a file in Python, what I am trying to do is something like this:
def test():
print("This is a Test")
file=open('Log','a')
file.write(test())
file.close()
But when I do this I get this error:
TypeError: argument 1 must be string or read-only character buffer, not None
PD: I'm trying to do this for a function I can't modify.
Whenever any operation would need to be performed in pairs, use a context manager.
In this case, use contextlib.redirect_stdout:
with open('Log','a') as f:
with contextlib.redirect_stdout(f):
test()
Edit: if you want it as a string, use io.StringIO:
f = io.StringIO()
with contextlib.redirect_stdout(f):
test()
s = f.getvalue()
python and there are a lot of people still using python 2.n despite what your preference may be.contextlib2 module on Pypi ... really, anyone still using Python2 should be used to hunting down backports.
You need to redirect the standard output by assigning it an object implementing the write method, like a file.
import sys
def test():
print("This is a Test")
stdout_backup = sys.stdout
with open('Log', 'a') as f:
sys.stdout = f
test()
sys.stdout = stdout_backup
Solution 1:
Instead of using print, you should use logging to do this:
import logging
logger = logging.getLogger('myapp')
hdlr = logging.FileHandler('/tmp/myapp.log')
logger.addHandler(hdlr)
logger.setLevel(logging.INFO)
def test():
logger.info("This is a Test")
test()
the codes above works fine, you can use it. PS: check the output in file /tmp/myapp.log
Solution 2:
just run your codes in command line, and store all the output into a file 'text.log'
python main.py >> text.log
Solution 3:
import contextlib
from contextlib import ExitStack
def test():
print('hello world')
with ExitStack() as stack:
f = stack.enter_context(open('Log', 'a'))
stack.enter_context(contextlib.redirect_stdout(f))
test()
print("I'm not logged")
you can define a decorator based on @o11c answer:
def redirect_output_to_file(fname, overwrite=False):
def real_redirect_output_to_file(func):
def wrapper(*args, **kwargs):
import contextlib
with open(fname, 'w' if overwrite else 'a') as f:
with contextlib.redirect_stdout(f):
retval = func(*args, **kwargs)
return retval
return wrapper
return real_redirect_output_to_file
And then use it on any function:
@redirect_output_to_file('test_output.log')
def test():
print('Hi')
Is the function in the same file? becuase it is was you could do something like this
Solution 1:
import sys
def test():
print("This is a test")
out = sys.stdout
with open("Log", "a") as output:
sys.stdout = output
test()
sys.stdout = out
gives
[Program finished]
contents in file,
This is a test
This is a test
The issue is that the function only prints, but doesn't return anything. Python 3.4 added https://docs.python.org/3/library/contextlib.html#contextlib.redirect_stdout which allows you to redirect stdout to a file:
Solution 2:
PS C:\Users\tan\Desktop> cat stdout.py
def test():
print("This is a Test")
from contextlib import redirect_stdout
with open('stdout.txt', 'w') as f:
with redirect_stdout(f):
test()
print('stdout in console again')
PS C:\Users\tan\Desktop> python .\stdout.py
stdout in console again
PS C:\Users\tan\Desktop> cat stdout.txt
This is a Test
