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diff --git a/python.html.markdown b/python.html.markdown index 6c9da9a9..55f56071 100644 --- a/python.html.markdown +++ b/python.html.markdown @@ -8,21 +8,21 @@ contributors: filename: learnpython.py --- -Python was created by Guido Van Rossum in the early 90s. It is now one of the -most popular languages in existence. I fell in love with Python for its +Python was created by Guido Van Rossum in the early 90s. It is now one of the +most popular languages in existence. I fell in love with Python for its syntactic clarity. It's basically executable pseudocode. -Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) +Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service] -Note: This article applies to Python 2.7 specifically, but should be applicable -to Python 2.x. Python 2.7 is reaching end of life and will stop being -maintained in 2020, it is though recommended to start learning Python with +Note: This article applies to Python 2.7 specifically, but should be applicable +to Python 2.x. Python 2.7 is reaching end of life and will stop being +maintained in 2020, it is though recommended to start learning Python with Python 3. For Python 3.x, take a look at the [Python 3 tutorial](http://learnxinyminutes.com/docs/python3/). -It is also possible to write Python code which is compatible with Python 2.7 +It is also possible to write Python code which is compatible with Python 2.7 and 3.x at the same time, using Python [`__future__` imports](https://docs.python.org/2/library/__future__.html). `__future__` imports -allow you to write Python 3 code that will run on Python 2, so check out the +allow you to write Python 3 code that will run on Python 2, so check out the Python 3 tutorial. ```python @@ -549,6 +549,10 @@ 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. Classes @@ -668,10 +672,10 @@ import math dir(math) # If you have a Python script named math.py in the same -# folder as your current script, the file math.py will -# be loaded instead of the built-in Python module. +# folder as your current script, the file math.py will +# be loaded instead of the built-in Python module. # This happens because the local folder has priority -# over Python's built-in libraries. +# over Python's built-in libraries. #################################################### @@ -679,44 +683,54 @@ dir(math) #################################################### # Generators -# A generator "generates" values as they are requested instead of storing +# A generator "generates" values as they are requested instead of storing # everything up front -# The following method (*NOT* a generator) will double all values and store it +# The following method (*NOT* a generator) will double all values and store it # in `double_arr`. For large size of iterables, that might get huge! def double_numbers(iterable): double_arr = [] for i in iterable: double_arr.append(i + i) -# Running the following would mean we'll double all values first and return all +# Running the following would mean we'll double all values first and return all # of them back to be checked by our condition for value in double_numbers(range(1000000)): # `test_non_generator` print value if value > 5: break -# We could instead use a generator to "generate" the doubled value as the item +# We could instead use a generator to "generate" the doubled value as the item # is being requested def double_numbers_generator(iterable): for i in iterable: yield i + i # Running the same code as before, but with a generator, now allows us to iterate -# over the values and doubling them one by one as they are being consumed by -# our logic. Hence as soon as we see a value > 5, we stop break out of the +# over the values and doubling them one by one as they are being consumed by +# our logic. Hence as soon as we see a value > 5, we break out of the # loop and don't need to double most of the values sent in (MUCH FASTER!) for value in double_numbers_generator(xrange(1000000)): # `test_generator` print value if value > 5: break -# BTW: did you notice the use of `range` in `test_non_generator` and `xrange` in `test_generator`? +# BTW: did you notice the use of `range` in `test_non_generator` and `xrange` in `test_generator`? # Just as `double_numbers_generator` is the generator version of `double_numbers` # We have `xrange` as the generator version of `range` # `range` would return back and array with 1000000 values for us to use # `xrange` would generate 1000000 values for us as we request / iterate over those items +# 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 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 |