Python Pocket Reference

Python Idioms and Hints

• S [:] makes a top-level copy of any sequence object; copy.deepcopy(X) makes full copies.

• L [:0] = [X,Y,Z ] inserts items at front of list L; L [len(L): ] = [X,Y,Z ] inserts at end (in-place “+”).

• Uses for key in D.keys( ): to iterate through dictionaries; uses K=D.keys( ); K.sort( ) to order.

• X = A or B or None assigns X to the first true object among A and B, or None if all are false (empty).

• X, Y = Y, X swaps the values of X and Y; red, green, blue = range(3) assigns integer series.

• Uses if __name__ == ‘__main__’: to add self-test code at the bottom of module files (true when run only).

• To make a file an executable script, add line at top like #!/usr/bin/env python or #!/usr/local/bin/python.

• Command-line arguments: sys.argv, environment: os.environ, streams: sys.stdin/stdout/stderror, filename expansion: glob.glob(“pattern”).

• To run shell commands: os.system(“cmd”), or output=os.popen(“cmd”).read( ), or os.fork/execv.

• The dir( [object ]) function is useful for inspecting attribute namespaces; __doc__ often is documentation.

• print and raw_input( ) use sys.stdout/stdin streams: assign to file-like objects to redirect I/O internally.

• See Python references and books for topics skipped here: Python/C integration API, Tkinter GUI API, Windows tools (COM/ActiveX), Internet modules, JPython, etc.

• Important web sites: http://www.python.org (Python home), http://rmi.net/~lutz (updates to this).

• You should always say “spam” and “eggs” instead of “foo” and “bar” in Python examples. ...