My Python World

Python World

                         

                      My Python World is to a discussion about python and features of the Python language. 

PyTrick

Trick:- 1

# Python's list slice syntax can be used without indices
# for a few fun and useful things:

# You can clear all elements from a list:
>>> lst = [1, 2, 3, 4, 5]
>>> del lst[:]
>>> lst
[]

# You can replace all elements of a list
# without creating a new list object:
>>> a = lst
>>> lst[:] = [7, 8, 9]
>>> lst
[7, 8, 9]
>>> a
[7, 8, 9]
>>> a is lst
True

# You can also create a (shallow) copy of a list:
>>> b = lst[:]
>>> b
[7, 8, 9]
>>> b is lst
False

Trick:- 2

# collections.Counter lets you find the most common

# elements in an iterable:

>>> import collections
>>> c = collections.Counter('helloworld')

>>> c
Counter({'l': 3, 'o': 2, 'e': 1, 'd': 1, 'h': 1, 'r': 1, 'w': 1})

>>> c.most_common(3)
[('l', 3), ('o', 2), ('e', 1)]

Trick:- 3

# Check if all elements in a list are equal

# Pythonic ways of checking if all
# items in a list are equal:

>>> lst = ['a', 'a', 'a']

>>> len(set(lst)) == 1
True

>>> all(x == lst[0] for x in lst)
True

>>> lst.count(lst[0]) == len(lst)
True

# I ordered those from "most Pythonic" to "least Pythonic" 
# and  "least efficient" to "most efficient". 
# The len(set()) solution is idiomatic,  but constructing 
# a set is less efficient memory and speed-wise.

Trick:- 4

# How to merge two dictionaries
# in Python 3.5+

>>> x = {'a': 1, 'b': 2}
>>> y = {'b': 3, 'c': 4}

>>> z = {**x, **y}

>>> z
{'c': 4, 'a': 1, 'b': 3}

# In Python 2.x you could
# use this:
>>> z = dict(x, **y)
>>> z
{'a': 1, 'c': 4, 'b': 3}

# In these examples, Python merges dictionary keys
# in the order listed in the expression, overwriting 
# duplicates from left to right.
#
# See: https://www.youtube.com/watch?v=Duexw08KaC8





Trick:- 5

# How to sort a Python dict by value
# (== get a representation sorted by value)

>>> xs = {'a': 4, 'b': 3, 'c': 2, 'd': 1}

>>> sorted(xs.items(), key=lambda x: x[1])
[('d', 1), ('c', 2), ('b', 3), ('a', 4)]

# Or:

>>> import operator
>>> sorted(xs.items(), key=operator.itemgetter(1))
[('d', 1), ('c', 2), ('b', 3), ('a', 4)]