[Type B] File Handling – Chapter 5 Sumita Arora
Table of Contents
13. What will be the output of the following code?
import pickle
List1 = ['Roza', {'a': 23, 'b': True}, (1, 2, 3), [['dogs', 'cats'], None] ]
List2 = ['Rita', {'x': 45, 'y': False}, (9, 5, 3), [['insects', 'bees'], None] ]
with open('data.pkl', 'wb') as f:
f.write(List1)
with open('data.pkl', 'wb') as f :
f.write(List2)
with open('data.pkl', 'rb') as f :
List1 = pickle.load(f)
print(List1)Answer: The given code contains an error that prevents it from producing the correct output.
The code first attempts to write two lists, List1 and List2, to the file “data.pkl” in binary mode. However, there is a critical error in this approach. The write() method of a file object in Python is designed to work with bytes, not entire Python objects. As a result, an error is shown.
Traceback (most recent call last):
File "incorrect_pickle_usage.py", line 5, in <module>
f.write(List1)
TypeError: expected bytes, not listHere’s a corrected version of the code that addresses this issue:
import pickle
List1 = ['Roza', {'a': 23, 'b': True}, (1, 2, 3), [['dogs', 'cats'], None] ]
List2 = ['Rita', {'x': 45, 'y': False}, (9, 5, 3), [['insects', 'bees'], None] ]
with open('data.pkl', 'wb') as f:
pickle.dump(List1 , f )
with open('data.pkl', 'wb') as f :
pickle.dump(List2 , f )
with open('data.pkl', 'rb') as f :
list1 = pickle.load(f)
print(list1)The output of this code:
['Rita', {'x': 45, 'y': False}, (9, 5, 3), [['insects', 'bees'], None]]Alternative Approach:
Where we store both the lists into the binary file rather than the last accessed one. More details on this below.
import pickle
List1 = ['Roza', {'a': 23, 'b': True}, (1, 2, 3), [['dogs', 'cats'], None]]
List2 = ['Rita', {'x': 45, 'y': False}, (9, 5, 3), [['insects', 'bees'], None]]
# Pickle both lists into a single byte stream
pickled_data = pickle.dumps([List1, List2])
# Open the file in binary write mode and write the pickled data
with open('data.pkl', 'wb') as f:
f.write(pickled_data)
# Open the file in binary read mode and read the pickled data back into a list
with open('data.pkl', 'rb') as f:
unpickled_data = pickle.load(f)
print(unpickled_data)This corrected code effectively serializes both List1 and List2 into a single byte stream using pickle.dumps(). It then writes this byte stream to the file “data.pkl”. When the file is opened for reading later, the pickled data is loaded back into a Python list using pickle.loads().
The output of this corrected code will be:
[['Roza', {'a': 23, 'b': True}, (1, 2, 3), [['dogs', 'cats'], None]], ['Rita', {'x': 45, 'y': False}, (9, 5, 3), [['insects', 'bees'], None]]]This demonstrates that the code successfully stores and retrieves the two lists using the pickle module.
Good work posting these questions in detail!