7.7. Files Binary¶

7.7.1. Rationale¶

Text I/O over a binary storage (such as a file) is significantly slower than binary I/O over the same storage
It requires conversions between unicode and binary data using a character codec
This can become noticeable handling huge amounts of text data like large log files
Source: https://docs.python.org/3/library/io.html#id3

7.7.2. Write Binary¶

mode='wb' - write in binary mode

FILE = r'/tmp/myfile.bin'
DATA = 'We choose to go to the Moon...'
data = DATA.encode()

with open(FILE, mode='wb') as file:
    file.write(data)

7.7.3. Append Binary¶

mode='ab' - append in binary mode

FILE = r'/tmp/myfile.bin'
DATA = 'We choose to go to the Moon...'
data = DATA.encode()

with open(FILE, mode='ab') as file:
    file.write(data)

7.7.4. Read Binary¶

mode='rb' - read in binary mode

FILE = r'/tmp/myfile.bin'

with open(FILE, mode='rb') as file:
    data = file.read()

result = data.decode()
print(result)

7.7.5. Pickle¶

Works with any Python object (variables, functions, classes, nested objects)

More information in Serialization Pickle

Listing 7.4. Write binary data to file¶

import pickle

FILE = r'/tmp/myfile.pkl'
data = [1, 2, 3]

with open(FILE, mode='wb') as file:
    pickle.dump(data, file)

Listing 7.5. Load binary data from file¶

import pickle

FILE = r'/tmp/myfile.pkl'

with open(FILE, mode='rb') as file:
    result = pickle.load(file)

print(result)

7.7.6. Seek¶

Go to the n-th byte in the file

Supports negative index (from end of file)

FILE = r'/tmp/myfile.bin'


with open(FILE, mode='wb') as file:
    file.write(b'0123456789abcdef')

with open(FILE, mode='rb') as file:
    file.seek(5)      # Go to the 6th byte in the file
    # 5

    file.read(1)
    # b'5'

    file.seek(-3, 2)  # Go to the 3rd byte before the end
    # 13

    file.read(1)
    # b'd'