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+--- Thread: get print() output (/thread-3000.html)
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get print() output - Skaperen - Apr-24-2017
i want to call a function and capture its print() output. so i was thinking to use the StringIO class. but when the function is ending and closes its output, StringIO destructs (whereas a real file would have its buffers flushed and be saved. i am looking for a better way to read the print output of the function after it does the close.
RE: get print() output - Mekire - Apr-24-2017
Not enough to just redirect stdout?
RE: get print() output - wavic - Apr-24-2017
I think he is doing just that.
Or maybe not. Are you using the print() file argument to redirect the output? Also, print() has a boolean flush argument. I am not really sure what it does.
You can pass the StringIO object to the function and use it as print(text, file=file_obj) argument
RE: get print() output - Mekire - Apr-24-2017
(Apr-24-2017, 06:57 AM)wavic Wrote: Are you using the print() file argument to redirect the output?I had assumed it was a case where this couldn't be altered. Like a black box function that prints stuff; in which case you would need to redirect stdout with the sys module or similar.
RE: get print() output - wavic - Apr-24-2017
from io import StringIO def my_func(out_file): text = "You won't see me." print(text, file=out_file) output = StringIO() my_func(output) out_text = output.getvalue()I was thinkging for something like this.
RE: get print() output - Mekire - Apr-24-2017
Was thinking this:
import sys
# Some function you can't change
def my_func():
text = "You won't see me."
print(text)
sys.stdout = open("sample.txt", "w")
my_func()
RE: get print() output - Skaperen - Apr-24-2017
(Apr-24-2017, 06:40 AM)Mekire Wrote: Not enough to just redirect stdout?
but how to redirect it back to the caller? what i am doing now is printing to stdout and piping that to another process that reads it. the other way i gave up on was printing to a file and reading it back. either too many processes or too slow when i have 600+ of these. since both parts are in python and one is a called function, there has to a more efficient way.
if there is a way to make StringIO not destroy on .close() that would solve it.
RE: get print() output - wavic - Apr-24-2017
In Python everything is an object.
Save it somewhere temporarily.
import sys stdout_bak = sys.stdout # some code sys.stdout = stdout_back
RE: get print() output - Skaperen - Apr-25-2017
(Apr-24-2017, 10:10 AM)wavic Wrote: In Python everything is an object.
Save it somewhere temporarily.
import sys stdout_bak = sys.stdout # some code sys.stdout = output_back
i'm assuming you meant for stdout_bak and output_back to be the same.
how do i get what the function that is called prints with the
print(file=foo) function after it is done? i can pass foo (a python file-like object) to the function. but the function closes it (e,g. it does foo.close()). i tried making foo be a StringIO object, but that fails because of the close.the function is in a module in .pyo format.
RE: get print() output - wavic - Apr-25-2017
(Apr-25-2017, 06:16 AM)Skaperen Wrote: i'm assuming you meant for stdout_bak and output_back to be the same.Right! I fixed it.
import sys
stdout_bak = sys.stdout
with open('output.txt', 'w') as sys.stdout:
print("I've never did this before so now I'm experimenting")
print("After that output.txt should containd this prints")
sys.stdout = stdout_bak # you must return everything as it was before to print normally again
print('After the first with statement')
with open('output.txt', 'r') as in_file:
print(in_file.read())Output:victor@jerry:~$ python3 /tmp/test.py
After the first with statement
I've never did this before so now I'm experimenting
After that output.txt should containd this prints