Mercurial > cpython-lru_cache-weakref

annotate Demo/classes/Range.py @ 80661:94de77bd0b4b 2.7

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Issue #16194: document imp.load_dynamic problems when read several extension modules from the same binary object file.
author Andrew Svetlov <andrew.svetlov@gmail.com>
date Thu, 29 Nov 2012 19:51:28 +0200
parents e371183d0e19
children 7d16b42fcdbd
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1 """Example of a generator: re-implement the built-in range function
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2 without actually constructing the list of values.
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3
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4 OldStyleRange is coded in the way required to work in a 'for' loop before
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5 iterators were introduced into the language; using __getitem__ and __len__ .
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6
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7 """
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8 def handleargs(arglist):
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9 """Take list of arguments and extract/create proper start, stop, and step
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10 values and return in a tuple"""
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11 try:
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12 if len(arglist) == 1:
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13 return 0, int(arglist[0]), 1
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14 elif len(arglist) == 2:
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15 return int(arglist[0]), int(arglist[1]), 1
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16 elif len(arglist) == 3:
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17 if arglist[2] == 0:
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18 raise ValueError("step argument must not be zero")
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19 return tuple(int(x) for x in arglist)
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20 else:
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21 raise TypeError("range() accepts 1-3 arguments, given", len(arglist))
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22 except TypeError:
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23 raise TypeError("range() arguments must be numbers or strings "
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24 "representing numbers")
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26 def genrange(*a):
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27 """Function to implement 'range' as a generator"""
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28 start, stop, step = handleargs(a)
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29 value = start
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30 while value < stop:
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31 yield value
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32 value += step
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33
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34 class oldrange:
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35 """Class implementing a range object.
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36 To the user the instances feel like immutable sequences
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37 (and you can't concatenate or slice them)
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38
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39 Done using the old way (pre-iterators; __len__ and __getitem__) to have an
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40 object be used by a 'for' loop.
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41
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42 """
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43
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44 def __init__(self, *a):
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45 """ Initialize start, stop, and step values along with calculating the
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46 nubmer of values (what __len__ will return) in the range"""
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47 self.start, self.stop, self.step = handleargs(a)
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48 self.len = max(0, (self.stop - self.start) // self.step)
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49
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50 def __repr__(self):
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51 """implement repr(x) which is also used by print"""
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52 return 'range(%r, %r, %r)' % (self.start, self.stop, self.step)
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53
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54 def __len__(self):
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55 """implement len(x)"""
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56 return self.len
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57
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58 def __getitem__(self, i):
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59 """implement x[i]"""
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60 if 0 <= i <= self.len:
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61 return self.start + self.step * i
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62 else:
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63 raise IndexError, 'range[i] index out of range'
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66 def test():
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67 import time, __builtin__
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68 #Just a quick sanity check
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69 correct_result = __builtin__.range(5, 100, 3)
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70 oldrange_result = list(oldrange(5, 100, 3))
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71 genrange_result = list(genrange(5, 100, 3))
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72 if genrange_result != correct_result or oldrange_result != correct_result:
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73 raise Exception("error in implementation:\ncorrect = %s"
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74 "\nold-style = %s\ngenerator = %s" %
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75 (correct_result, oldrange_result, genrange_result))
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76 print "Timings for range(1000):"
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77 t1 = time.time()
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78 for i in oldrange(1000):
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79 pass
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80 t2 = time.time()
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81 for i in genrange(1000):
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82 pass
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83 t3 = time.time()
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84 for i in __builtin__.range(1000):
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85 pass
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86 t4 = time.time()
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87 print t2-t1, 'sec (old-style class)'
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88 print t3-t2, 'sec (generator)'
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89 print t4-t3, 'sec (built-in)'
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92 if __name__ == '__main__':
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93 test()