CODEWITHSUNDEEP
pythonserializationpicklepython-3.2
Sergey
Sergey

Reputation: 49728

Usage of pickle.dump in Python

I'm trying to learn how to use the pickle module in Python:

import pickle
x = 123
f = open('data.txt','w')
pickle.dump(x,f)

Here's what I get:

Traceback (most recent call last):
  File "D:\python\test.py", line 5, in <module>
    pickle.dump(x,f)
TypeError: must be str, not bytes

However, this code works just fine:

import pickle
dump = pickle.dump(123)
print(dump)


What am I doing wrong?

Upvotes: 29

Views: 45365

Answers (2)

garnertb
garnertb

Reputation: 9584

The write method for file-like objects, only accept a single string argument. The dumps method in the pickle module automatically casts arguments as strings, whereas the the dump method will write a pickled representation of the object to the open file. Since 123 is not a string it throws the TypeError error.

This is acknowledged in pickle.dump documentation.

Upvotes: 2

DSM
DSM

Reputation: 352979

The problem is that you're opening the file in text mode. You need to use binary here:

>>> f = open('data.txt','w')
>>> pickle.dump(123,f)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: must be str, not bytes
>>> 
>>> f = open('data.txt','wb')
>>> pickle.dump(123,f)
>>>

Upvotes: 43

Related Questions