• PythonTips

PythonTips

A great reference sheet is at http://rgruet.free.fr/PQR2.3.html

• = Strings =

• Join items in list into string with space separators:

     ' '.join(list) 

  = List Comprehensions =

• Create list of integers in a range:

     [i for i in range(4)] 

• Create a 2-D Array:

     w,h = 2,3
     A = [ [None]*w for i in range(h) ] 

• Create list of lines of output from shell command:

     [os.popen('SHELL_COMMAND').read().split('\n')] 

• List of Qualified Names:

     [file[:-1] for file in os.popen(COMMAND) if pattern infile] 

  = Slicings =

   Sequence slicing [starting-at-index :  but-less-than-index [ : step]].
   Start defaults to 0, end to len(sequence), step to 1.
  
    a = (0,1,2,3,4,5,6,7)
    a[3] == 3
    a[-1] == 7
    a[2:4] == (2, 3)
    a[1:] == (1, 2, 3, 4, 5, 6, 7)
    a[:3] == (0, 1, 2)
    a[:] == (0,1,2,3,4,5,6,7) # makes a copy of the sequence.
    a[::2] == (0, 2, 4, 6) # Only even numbers. 
    a[::-1] = (7, 6, 5, 4, 3 , 2, 1, 0) # Reverse order.
   

  = File System =
• os.path.isfile(FILE)
• os.path.isdir(FILE)
• (base, ext) = os.path.splitext(FILE)

• Walk thru all lines of file

     for line in open('FILE').readlines() 

• glob.glob('*.jpg')