理解Shebang line: #!/usr/bin/python3

• Overview

  From google styleguide, Most .py files do not need to start with a #! line.

  Start the main file of a program with #!/usr/bin/env python3 (to support virtualenvs) or #!/usr/bin/python3 per PEP-394.

  This line is used by the kernel to find the Python interpreter, but is ignored by Python when importing modules.

  It is only necessary on a file intended to be executed directly.

• Shebang

  A shebang(sha-bang, hashbang, pound-bang, hash-pling) is the character sequence consisting consisting of the characters number sign and exclamation mark (#!) at the beginning of a script.

  When a text file with a shebang is used as if it is an execuable in a Unix-like OS, the program loader mechanism parses the rest of the file’s inital line as an interpreter directive.

  The form of a shebang interpreter directive is as follow:

  #!interpreter [optional-arg]