python-Slicing Iteration Builder

1-Slice operation

>>>l['AAA','BBB','CCC','DDD']>>> L[0:3]['AAA','BBB','CCC']>>> L[::5][0,5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95]0-100 of all numbers, every 5 take one

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2 iterative operations You can iterate as long as you have an iterative object

1>>> d = {'a': 1,'b': 2,'C': 3}2>>> forKeyinchD:3...PrintKey4 ...5 a6 C7B

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Iterate the default iteration key for a dictionary if you want to iterate over a value, you can use the following code

1>>>D2{'a': 1,'C': 3,'b': 2}3>>> forValuesinchd.itervalues ():4...PrintValues5 ...617382

View Code d.itervalues () an iterative object that returns a dictionary value
iterate keys and values at the same time:

1  for inch D.iteritems (): 2 ...     Print K, v 3 ... 4 a 15 c 36 B 2

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2.1 Judging an Iterative object

1  from Import iterable 2 >>> isinstance (D.iteritems (), iterable)3 True

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The 2.3 Enumerate function can turn a list into an index-element pair so that both the index and the element itself can be iterated in the For loop

 1  >>> for  i, v in  Enumerate ([  a  , "  b  ,  '  c   '  

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2.4 List-generated

1  for  in range (1, one)]2 [1, 4, 9, +,,, +, +, Bayi, +]3 The X*X elements that need to be generated are placed in front

View Code 3 GeneratorsThe process of generating a list is based on the calculation formula, and the edge is calculated as the edge is generated instead of one generation at a time 3.1 To change a list-generated [] to (), create a generator

1  for  in range (ten)]2 >>> L3 [0, 1, 4, 9, +,- C8>4 list generation vs. generator comparison 5 for in range (ten))6 >> > g7 <generator object <genexpr> at 0x7f87935774b0>

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The next () method of the generator makes it easy to generate subsequent elements, all printing requires a For loop variable

1>>>G.next ()2 03>>>G.next ()415>>>G.next ()647>>>G.next ()899>>> forNinchg:Ten...PrintN One ... A16 -25 -36 the49 -64 -81

View Code 3.2 The generator function can also be used with yield generate a generator function by yield as follows

1 def fib (max): 2 ...     N, a, b = 0, 0, 13     ...  while (N < max): 4 ...             yield b 5 ...             A, B = A, a + b6             ... n = n + 17... 8 >>> fib (6)9 <generator object fib at 0x7f8793577aa0>

View CodeThe generator function executes differently from the normal function, and each time the generator function is generated, it executes at the last yield .The code example is as follows:

1>>>defOdd ():2...Print 'Step 1'3...yield14...Print 'Step 2'5...yield26...Print 'Step 3'7...yield38 ...9>>> o =Odd ()Ten>>>O.next () OneStep 1 A1 ->>>O.next () -Step 2 the2 ->>>O.next () -Step 3 -3

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python-Slicing Iteration Builder