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aritprog_v1.py
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"""
Arithmetic progression class
# BEGIN ARITPROG_CLASS_DEMO
>>> ap = ArithmeticProgression(0, 1, 3)
>>> list(ap)
[0, 1, 2]
>>> ap = ArithmeticProgression(1, .5, 3)
>>> list(ap)
[1.0, 1.5, 2.0, 2.5]
>>> ap = ArithmeticProgression(0, 1/3, 1)
>>> list(ap)
[0.0, 0.3333333333333333, 0.6666666666666666]
>>> from fractions import Fraction
>>> ap = ArithmeticProgression(0, Fraction(1, 3), 1)
>>> list(ap)
[Fraction(0, 1), Fraction(1, 3), Fraction(2, 3)]
>>> from decimal import Decimal
>>> ap = ArithmeticProgression(0, Decimal('.1'), .3)
>>> list(ap)
[Decimal('0.0'), Decimal('0.1'), Decimal('0.2')]
# END ARITPROG_CLASS_DEMO
"""
# BEGIN ARITPROG_CLASS
class ArithmeticProgression:
def __init__(self, begin, step, end=None): # <1>
self.begin = begin
self.step = step
self.end = end # None -> "infinite" series
def __iter__(self):
result = type(self.begin + self.step)(self.begin) # <2>
forever = self.end is None # <3>
index = 0
while forever or result < self.end: # <4>
yield result # <5>
index += 1
result = self.begin + self.step * index # <6>
# END ARITPROG_CLASS