1. Binary Files

2. Overview
Text file are convenient because you can read and change them using any text editor
However, text files are limited to only text characters
Sometimes you need to store more complex data structures
Binary files allow you to store list and dictionary data structures
You can’t change binary files with a text editor

3. Pickle In Python, pickling is a means to preserve complex data
You can write lists or dictionaries
For pickled data, you must read in the same order written
You must ‘import pickle’ to gain access to the pickle code

4. Selected Binary File Access Modes
“rb” Read from a binary file. If the file doesn’t exist, Python will complain with an error
“wb” Write to a binary file. If the file exists, its contents are overwritten. If the file doesn’t exist, it’s created
“ab” Append a binary file. If the file exists, new data is appended to it. If the file doesn’t exist, it’s created.
More access modes on page 201 of your book

5. Selected Pickle Functions
dump(object, file, [,bin]) Writes pickled version of object to a file. If bin is True, object is written in binary format. If bin is False, object is written in less efficient, but more human-readable text format. The default is False
load(file) Unpickles and returns the next pickled object in file

6. Simple Example variety = ["sweet", "hot", "dill"] # Create the list
file = open("myPickle.dat", "wb") # Create the binary file
pickle.dump(variety, file) # Write the list to file
file.close() # Close the file
file = open(PICKLE_PATH, "rb") # Open the file for read
variety = pickle.load(file) # Read the file
print("Variety: ", variety) # Print the list

7. Shelve Shelve also stores binary data Used for object persistence
When you shelve an object, you must give a key by which the object is known
This way, shelve becomes a database of stored values, any of which can be accessed at any time
You must use ‘import shelve’ to gain access to the Python shelve code

8. Selected Shelve Access Modes
“c” Open a file for reading or writing. If the file doesn’t exist it is created.
“n” Create a new file for reading or writing. If the file exists, it’s contents are overwritten.
“r” Read from a file. If the file doesn’t exist, Python will complain with an error.

9. Simple Shelve Example
file = shelve.open(“foo.dat”, “n”) # Create the file
file[“baseballScores”] = { “Rangers” : 1, “Astros” : 2} # Write
file.sync() # Flush to disk
file.close() # Close the file
file = shelve.open(“foo.dat”, “r”) # Open the file
print(file[“baseballScores”]) # Access by key

10. Complete Examples