TypeError: write() argument must be str, not bytes (Python 3 vs Python 2 )

Question

The below code works perfectly for python 2.7.13

import os
with open('random.bin','w') as f:
    f.write(os.urandom(10))

But throws error for python 3 3.6.0 |Anaconda 4.3.0 (64-bit)| (default, Dec 23 2016, 11:57:41) [MSC v.1900 64 bit (AMD64)]

Traceback (most recent call last): File "C:/Users/hsingh/PycharmProjects/Item3.py", line 3, in f.write(os.urandom(10)) TypeError: write() argument must be str, not bytes

Any reason why there is difference in behaviour or how to fix this

Same error I got in online compiler rextester.com/l/python3_online_compiler — Hariom Singh
– Hariom Singh, Commented Oct 31, 2017 at 3:15
I'm sure you'll find plenty of ways to fix this by googling "python write bytes to file" — jonatan
– jonatan, Commented Oct 31, 2017 at 3:17

Mark Ransom · Accepted Answer · 2017-10-31 03:21:12Z

45

In Python 3 it makes a difference whether you open the file in binary or text mode. Just add the b flag to make it binary:

with open('random.bin','wb') as f:

This works in Python 2 too.

answered Oct 31, 2017 at 3:21

Mark Ransom

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