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. 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)
  30
  

7.7.3. 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)
  30
  

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)
  We choose to go to the Moon...
  

7.7.5. Pickle

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

• More information in Serialization Pickle

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)

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)
[1, 2, 3]

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'
  >>> DATA = b'We choose to go to the Moon...'
  >>>
  >>>
  >>> with open(FILE, mode='wb') as file:
  ...    file.write(DATA)
  30
  >>>
  >>> file = open(FILE, mode='rb')
  >>>
  >>> file.seek(23)
  23
  >>> file.read(1)
  b'M'
  >>> file.read(1)
  b'o'
  >>> file.read(1)
  b'o'
  >>> file.read(1)
  b'n'
  >>>
  >>> file.seek(23)
  23
  >>> file.read(4)
  b'Moon'
  >>>
  >>> file.seek(-7, 2)
  23
  >>> file.read(4)
  b'Moon'