Python redirect print output to file over loop

Question

Simple questions but it's annoying me. I'm attempting to loop over a series of products of varying factors and then print each product to a file. I can get the code to work using the "with" statement but can't get it to work without it and I can't understand why. I am opening the file and then closing it as usual. Code is as follows:

f = open('out.txt', 'w')
for num1 in range(100,999):
    for num2 in range(100,999):
        product=num1*num2
        length=len(str(product))
        if length % 2 == 0:
            #halfway_point=
            print >> f, product
f.close()

It is failing on the last line with:

SyntaxError: invalid syntax

Do you really have print >> f, product?

DavidG
– DavidG

2017-07-21 10:57:05 +00:00
Commented Jul 21, 2017 at 10:57 — DavidG
– DavidG, Commented Jul 21, 2017 at 10:57

mhawke · Accepted Answer · 2017-07-21 11:39:27Z

2

Not sure whether you are using Python 2 or Python 3. Either way, the fact that you see a SyntaxError suggests that an interactive interpreter session is being used.

I am going to assume that you are using Python 2. print >> expression, expression is a valid print statement in Python 2, and your usage of it in your code is correct. It simply means to redirect the string value of the second expression in the print statement to the file-like object given in the first expression. This statement is not available in Python 3.

Probably you are pasting the code into an interactive Python session, and if so you will need to add an extra new line to "close" the previous for loop before executing the close(), otherwise you will get a SyntaxError.

It will work if you add that code to a Python 2 script file and run it:

$ python2 somefile.py

or simply make sure to enter an extra new line if using the interactive interpreter.

For Python 3 you would do this:

print('{}'.format(product), file=f)

You can also use the same print() function in Python 2 by importing it from the __future__ module:

from __future__ import print_function

In both cases you should use the with statement as you mention in your question.

edited Jul 21, 2017 at 11:39

answered Jul 21, 2017 at 11:24

mhawke

87.5k10 gold badges122 silver badges142 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

dodgerstjw Over a year ago

Hi mhawke - thanks for this. You described the issue perfectly. Version is 2.7.10 but I was running in an interpreter which was causing it to fail after the loop - why does the interpreter need that extra line to close it?

mhawke Over a year ago

@dodgerstjw: check this answer for an explanation.

Md. Rezwanul Haque · Accepted Answer · 2017-07-21 11:19:14Z

0

I don't know what print >> f, product means. But you can try this way :

f = open('out.txt', 'w')
for num1 in range(100,999):
    for num2 in range(100,999):
        product=num1*num2
        length=len(str(product))
        if length % 2 == 0:
              #halfway_point=
              # print >> f, product
              print(str(product) ) # print in the console
              f.write(str(product) + "\n")
f.close()

edited Jul 21, 2017 at 11:19

answered Jul 21, 2017 at 11:12

Md. Rezwanul Haque

2,9487 gold badges35 silver badges49 bronze badges

Comments

Rahul · Accepted Answer · 2017-07-21 11:17:27Z

-1

Your Syntax error is coming because of print >> f, product

Moreover you are not writing to file but printing to console.

You need f.write(str(product) + '\n') line instead of print >> f, product (I don't know what print >> f, product means)

This works just fine for me in python3

f = open('out.txt', 'w')
for num1 in range(100,999):
    for num2 in range(100,999):
        product=num1*num2
        length=len(str(product))
        if length % 2 == 0:
            #halfway_point=
            f.write(str(product) + '\n')
f.close()

edited Jul 21, 2017 at 11:17

answered Jul 21, 2017 at 11:02

Rahul

11.7k5 gold badges63 silver badges100 bronze badges

Collectives™ on Stack Overflow

Python redirect print output to file over loop

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related