12.6. Files Binary¶
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
12.6.1. 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
12.6.2. 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)
30
12.6.3. 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...
12.6.4. 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]
12.6.5. 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'