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-   -   Code Snippet: Find pediodicity in a list (http://www.daniweb.com/forums/thread217248.html)

slate Jan 20th, 2009 5:29 pm
Find pediodicity in a list
 
A brute force method.
Finds the FIRST and SHORTEST periodicity in the input list.
 

  1. def find_period(inp):
  2.     '''
  3.     Finds the FIRST and SHORTEST periodicity in the list: inp. 
  4.     Returns the position of the 0-based begin of the periodicity if any, and the length of it
  5.     If it does not find any, returns None
  6.     '''
  7.     pos=0
  8.     other=1
  9.     adjust=0
  10.     leninp=len(inp)
  11.     while pos<leninp:
  12.         try:
  13.             other=inp.index(inp[pos],pos+1+adjust)
  14.         except ValueError:
  15.             other=None
  16.         if other and other-pos<=leninp-other:
  17.             for i in xrange(other,leninp):
  18.                 if inp[i-(other-pos)]!=inp[i]:
  19.                     adjust+=1
  20.                     break
  21.             else:
  22.                 return pos, other-pos
  23.         else:
  24.             adjust=0
  25.             pos+=1

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