Library in python

• In Python, there are many libraries you can use for free.
• To use library, you need to import.

Importing library

• Simple example;

  import numpy
  
  a = numpy.zeros(10)
  

• You can make abbriviation to library, as

  import numpy as np
  
  a = np.zeros(10)
  

pip

• If your computer doesn't have a library you want to use, install it using pip, which is a package manager.
• Any packages in PyPI (https://pypi.org/) is available.
• This shoud be done outside the Python interpreter or script (that is, terminal).

  pip install numpy
  

• In Jupyter notebook (Google colab), do like

  !pip install numpy
  

• To update some library,

  pip install numpy --update
  

os module (file and directory operations)

• The os module provides functions for interacting with the operating system.

  import os
  
  # Get current working directory
  cwd = os.getcwd()
  
  # Join path components
  path = os.path.join("data", "images", "photo.jpg")
  
  # Get file extension
  name, ext = os.path.splitext("photo.jpg")
  print(ext)  # => .jpg
  
  # Get absolute path
  abs_path = os.path.abspath("data")
  

• os.walk iterates through all directories and files recursively:

  import os
  
  for dirpath, dirnames, filenames in os.walk("data"):
      for filename in filenames:
          full_path = os.path.join(dirpath, filename)
          print(full_path)
  

• This is useful for finding all files in a directory tree.