python: get the print output in an exec statement

user_462794 0
Viewed 36012

I want to get the output of an exec(...) Here is my code:

code = """
i = [0,1,2]
for j in i :
    print j
"""
result = exec(code)

How could I get the things that print outputed? How can I get something like:

0
1
2

Regards and thanks.

exec printing python
7 Answers

Here is a small correction of Frédéric's answer. We need to handle a possible exception in exec() to return back normal stdout. Otherwise we could not see farther print outputs:

code = """
i = [0,1,2]
for j in i :
print j
"""

from cStringIO import StringIO
old_stdout = sys.stdout
redirected_output = sys.stdout = StringIO()
try:
    exec(code)
except:
    raise 
finally: # !
    sys.stdout = old_stdout # !

print redirected_output.getvalue()
...
print 'Hello, World!' # now we see it in case of the exception above
user_7492880

Python 3: Get the output of the exec into a variable

import io, sys
print(sys.version)

#keep a named handle on the prior stdout 
old_stdout = sys.stdout 
#keep a named handle on io.StringIO() buffer 
new_stdout = io.StringIO() 
#Redirect python stdout into the builtin io.StringIO() buffer 
sys.stdout = new_stdout 

#variable contains python code referencing external memory
mycode = """print( local_variable + 5 )""" 

local_variable = 2
exec(mycode)

#stdout from mycode is read into a variable
result = sys.stdout.getvalue().strip()

#put stdout back to normal 
sys.stdout = old_stdout 
 
print("result of mycode is: '" + str(result) + "'")

Prints:

3.4.8
result of mycode is: '7'

Also a reminder that python exec(...) is evil and bad because 1. It makes your code into unreadable goto-spaghetti. 2. Introduces end-user code injection opportunities, and 3. Throws the exception stacktrace into chaos because exec is made of threads and threads are bad mmkay.

user_4451310

You could combine exec with eval to get an output as list:

ExecString('i = [0,1,2]');
println(EvalStr('[j for j in i]'));
user_90412240
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