How to save and load objects to and from file in Python via facilities from the pickle module

There are times when it is more convenient for us to choose object serialization over database management systems for the persistency of the data that our Python scripts work with.

In this post, I document how we can save and load objects to and from file in Python using facilities from the pickle module.

Saving objects to file in Python

To save objects to file in Python, we typically go through the following steps:

1. Import the pickle module.
2. Get a file handle in write mode that points to a file path.
3. Use pickle.dump to write the object that we want to save to file via that file handle.

With these steps in mind, let's us create a Python script, save_dictionary_to_file.py, with the following Python codes:

# Step 1
import pickle

config_dictionary = {'remote_hostname': 'google.com', 'remote_port': 80}

# Step 2
with open('config.dictionary', 'wb') as config_dictionary_file:

  # Step 3
  pickle.dump(config_dictionary, config_dictionary_file)

In step 1, we import the pickle module with the import keyword.

In step 2, we use the with keyword and the open function to create a file handle that points to config.dictionary in the same directory where we will run save_dictionary_to_file.py.

The first string that we supply to the open function denotes the filepath to write our dictionary of values. The second string that we supply to the open function indicates that we want a file handle that writes binary contents to the file.

The with keyword ensures that the file handle generated by the open function is closed after our dictionary is serialized to file.

Finally in step 3, we use the pickle.dump function to write the contents of our dictionary to a file that will be named as config.dictionary.

After running save_dictionary_to_file.py, we should be able to see the config.dictionary file in the same directory where we run our Python script.

Loading objects from file in Python

To load the object from file in Python, we typically go through the following steps:

1. Import the pickle module.
2. Get a file handle in read mode that points to a file path that has a file that contains the serialized form of a Python object.
3. Use pickle.load to read the object from the file that contains the serialized form of a Python object via the file handle.

With these steps in mind, let us create a Python script, load_dictionary_from_file.py with the following Python codes:

# Step 1
import pickle

# Step 2
with open('config.dictionary', 'rb') as config_dictionary_file:

    # Step 3
    config_dictionary = pickle.load(config_dictionary_file)

    # After config_dictionary is read from file
    print(config_dictionary)

Similar to writing the dictionary to file, we import the pickle module in step 1.

In step 2, we use the with keyword with the open function to get a file handle that points to config.dictionary in the same directory where we will run load_dictionary_from_file.py.

As with saving the dictionary to file, we supply config.dictionary as the first input to the open function to indicate the file path to the file which contains the serialized dictionary. This time round, we supply the string 'rb' instead of 'wb' to indicate that we want a file handle that reads binary contents from the file.

Finally in step 3, we load the dictionary from the file to the config_dictionary variable via the pickle.load function.

Once we had loaded the dictionary from the file to the config_dictionary variable, we use the print function to print the dictionary contents to the standard output.

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