From e053806775d18e14bb5de2adcdf8369d6566ce45 Mon Sep 17 00:00:00 2001 From: "J. Ryan Rembert" Date: Sun, 3 Jul 2016 01:47:57 -0700 Subject: [python/en] Set, dict, and generator comprehensions (#2298) * Add set and dict comprehensions for python 2 and 3 * Clean up formatting and generator explanation * Include documentation for generator comprehensions --- python3.html.markdown | 38 ++++++++++++++++++++++++-------------- 1 file changed, 24 insertions(+), 14 deletions(-) (limited to 'python3.html.markdown') diff --git a/python3.html.markdown b/python3.html.markdown index 7f3702e6..6b3486a6 100644 --- a/python3.html.markdown +++ b/python3.html.markdown @@ -601,6 +601,10 @@ list(filter(lambda x: x > 5, [3, 4, 5, 6, 7])) # => [6, 7] [add_10(i) for i in [1, 2, 3]] # => [11, 12, 13] [x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7] +# You can construct set and dict comprehensions as well. +{x for x in 'abcddeef' if x in 'abc'} # => {'d', 'e', 'f'} +{x: x**2 for x in range(5)} # => {0: 0, 1: 1, 2: 4, 3: 9, 4: 16} + #################################################### ## 5. Modules @@ -816,7 +820,7 @@ if __name__ == '__main__': sup.age = 100 print(sup.age) - # Inherited attribute from 2nd ancestor whose default value was overriden + # Inherited attribute from 2nd ancestor whose default value was overridden. print('Can I fly? ' + str(sup.fly)) @@ -825,29 +829,35 @@ if __name__ == '__main__': ## 7. Advanced #################################################### -# Generators help you make lazy code +# Generators help you make lazy code. def double_numbers(iterable): for i in iterable: yield i + i -# A generator creates values on the fly. -# Instead of generating and returning all values at once it creates one in each -# iteration. This means values bigger than 15 wont be processed in -# double_numbers. -# We use a trailing underscore in variable names when we want to use a name that -# would normally collide with a python keyword -range_ = range(1, 900000000) -# will double all numbers until a result >=30 found -for i in double_numbers(range_): +# Generators are memory-efficient because they only load the data needed to +# process the next value in the iterable. This allows them to perform +# operations on otherwise prohibitively large value ranges. +# NOTE: `range` replaces `xrange` in Python 3. +for i in double_numbers(range(1, 900000000)): # `range` is a generator. print(i) if i >= 30: break +# Just as you can create a list comprehension, you can create generator +# comprehensions as well. +values = (-x for x in [1,2,3,4,5]) +for x in values: + print(x) # prints -1 -2 -3 -4 -5 to console/terminal + +# You can also cast a generator comprehension directly to a list. +values = (-x for x in [1,2,3,4,5]) +gen_to_list = list(values) +print(gen_to_list) # => [-1, -2, -3, -4, -5] + # Decorators -# in this example beg wraps say -# Beg will call say. If say_please is True then it will change the returned -# message +# In this example `beg` wraps `say`. If say_please is True then it +# will change the returned message. from functools import wraps -- cgit v1.2.3