72 lines
1.8 KiB
Python
Executable File
72 lines
1.8 KiB
Python
Executable File
# Example of a generator: re-implement the built-in range function
|
|
# without actually constructing the list of values. (It turns out
|
|
# that the built-in function is about 20 times faster -- that's why
|
|
# it's built-in. :-)
|
|
|
|
|
|
# Wrapper function to emulate the complicated range() arguments
|
|
|
|
def range(*a):
|
|
if len(a) == 1:
|
|
start, stop, step = 0, a[0], 1
|
|
elif len(a) == 2:
|
|
start, stop = a
|
|
step = 1
|
|
elif len(a) == 3:
|
|
start, stop, step = a
|
|
else:
|
|
raise TypeError, 'range() needs 1-3 arguments'
|
|
return Range(start, stop, step)
|
|
|
|
|
|
# Class implementing a range object.
|
|
# To the user the instances feel like immutable sequences
|
|
# (and you can't concatenate or slice them)
|
|
|
|
class Range:
|
|
|
|
# initialization -- should be called only by range() above
|
|
def __init__(self, start, stop, step):
|
|
if step == 0:
|
|
raise ValueError, 'range() called with zero step'
|
|
self.start = start
|
|
self.stop = stop
|
|
self.step = step
|
|
self.len = max(0, int((self.stop - self.start) / self.step))
|
|
|
|
# implement `x` and is also used by print x
|
|
def __repr__(self):
|
|
return 'range' + `self.start, self.stop, self.step`
|
|
|
|
# implement len(x)
|
|
def __len__(self):
|
|
return self.len
|
|
|
|
# implement x[i]
|
|
def __getitem__(self, i):
|
|
if 0 <= i < self.len:
|
|
return self.start + self.step * i
|
|
else:
|
|
raise IndexError, 'range[i] index out of range'
|
|
|
|
|
|
# Small test program
|
|
|
|
def test():
|
|
import time, __builtin__
|
|
print range(10), range(-10, 10), range(0, 10, 2)
|
|
for i in range(100, -100, -10): print i,
|
|
print
|
|
t1 = time.time()
|
|
for i in range(1000):
|
|
pass
|
|
t2 = time.time()
|
|
for i in __builtin__.range(1000):
|
|
pass
|
|
t3 = time.time()
|
|
print t2-t1, 'sec (class)'
|
|
print t3-t2, 'sec (built-in)'
|
|
|
|
|
|
test()
|