Functional Programming
A pure function does not modify any of the objects passed.
# Pure function ...
#
# does not modify any of the objects passed and ...
# has no side effects, like displaying a value or getting an input
class Hour:
"""Represents the day time
attributes: hour
"""
def increment_pure(t, d):
sum = Hour()
sum.hour = t.hour + d.hour
return sum
def increment_impure(t, d):
sum = Hour()
sum.hour = t.hour + int(d.hour) # Look Here
return sum
start = Hour()
start.hour = 9.0
duration = Hour()
duration.hour = 1.5
end = increment_pure(start, duration) # Correct
assert end.hour == 10.5
assert end.hour != 10
end = increment_impure(start, duration) # Wrong
assert end.hour != 10.5
assert end.hour == 10
# Side efects
end = increment_pure(start, duration) # Correct
def print_time(obj): # impure - side efects
print('%.2d' % obj.hour) # 2 digits
print_time(end) # 10
Modifiers
Functions that modifiy the objects are called modifiers.
# Modifiers
#
# Functions that modifiy the objects are called modifiers.
#
# Pure functions are faster to develop and less error-prone, but ...
# modifiers are convenient at times and efficient.
class Time: pass
def increment(t, seconds): # modifier
t.seconds = t.seconds + seconds
def increment_pure(seconds): # pure
time = Time()
minutes, time.seconds = divmod(seconds, 60)
hour, time.minutes = divmod(minutes, 60)
time.hour = hour
return time
def print_time(t):
print('%.2d:%.2d:%.2d' % (t.hour, t.minutes, t.seconds))
t = Time()
t.hour = 9
t.minutes = 45
t.seconds = 0
increment(t, 20)
print_time(t)
# 10:45:20
t = increment_pure(160)
print_time(t)
# 00:02:40
Last update: 260 days ago
