The following are just a collection of some useful shortcuts and tools I’ve found in Python over the years. Hopefully you find them helpful.
more advance pyDuffers like me can look here vjex/PyTricks
Swapping Variables
x = 6
y = 5
x, y = y, x
print x
>>> 5
print y
>>> 6
Inline if Statement
print "Hello" if True else "World"
>>> Hello
Concatenations
The last one is a pretty cool way to combine objects of two different types.
nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
print nfc + afc
>>> ['Packers', '49ers', 'Ravens', 'Patriots']
print str(1) + " world"
>>> 1 world
print `1` + " world"
>>> 1 world
print 1, "world"
>>> 1 world
print nfc, 1
>>> ['Packers', '49ers'] 1
Number Tricks
#Floor Division (rounds down)
print 5.0//2
>>> 2
#2 raised to the 5th power
print 2**5
>> 32
Be careful with division and floating point numbers.
print .3/.1
>>> 2.9999999999999996
print .3//.1
>>> 2.0
Numerical Comparison This is a pretty cool shortcut that I haven’t seen in too many languages.
x = 2
if 3 > x > 1:
print x
>>> 2
if 1 < x > 0:
print x
>>> 2
Iterate Through Two Lists at the Same Time
nfc = ["Packers", "49ers"]
afc = ["Ravens", "Patriots"]
for teama, teamb in zip(nfc, afc):
print teama + " vs. " + teamb
>>> Packers vs. Ravens
>>> 49ers vs. Patriots
Iterate Through List With an Index
teams = ["Packers", "49ers", "Ravens", "Patriots"]
for index, team in enumerate(teams):
print index, team
>>> 0 Packers
>>> 1 49ers
>>> 2 Ravens
>>> 3 Patriots
List Comprehension
With a list comprehension we can turn this:
numbers = [1,2,3,4,5,6]
even = []
for number in numbers:
if number%2 == 0:
even.append(number)
Into this:
numbers = [1,2,3,4,5,6]
even = [number for number in numbers if number%2 == 0]
Pretty sweet huh?
Dictionary Comprehension
Similar to the list comprehension we can also do a dictionary comprehension like this:
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print {key: value for value, key in enumerate(teams)}
>>> {'49ers': 1, 'Ravens': 2, 'Patriots': 3, 'Packers': 0}
Initialize List Values
items = [0]*3
print items
>>> [0,0,0]
Converting a List to a String
teams = ["Packers", "49ers", "Ravens", "Patriots"]
print ", ".join(teams)
>>> 'Packers, 49ers, Ravens, Patriots'
Get Item From Dictionary
I’ll admit that try/except code doesn’t look the prettiest. Here’s a simple way to fix that with dictionaries. This will try to find the key in the dictionary and if it can’t be found it will set the variable to the second parameter. Instead of:
data = {'user': 1, 'name': 'Max', 'three': 4}
try:
is_admin = data['admin']
except KeyError:
is_admin = False
Do this:
data = {'user': 1, 'name': 'Max', 'three': 4}
is_admin = data.get('admin', False)
Taking a Subset of a List
Sometimes you only want to run code over a portion of a list. Here are a few ways you can get the subset of a list.
x = [1,2,3,4,5,6]
#First 3
print x[:3]
>>> [1,2,3]
#Middle 4
print x[1:5]
>>> [2,3,4,5]
#Last 3
print x[-3:]
>>> [4,5,6]
#Odd numbers
print x[::2]
>>> [1,3,5]
#Even numbers
print x[1::2]
>>> [2,4,6]
FizzBuzz in 60 Characters
Here’s a short, fun way to solve the problem.
for x in range(1,101):print"Fizz"[x%3*4:]+"Buzz"[x%5*4:]or x
Collections
In addition to python’s built in datatypes they also include a few extra for special use cases in the collections module.
from collections import Counter
print Counter("hello")
>>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})
Itertools
Along with the collections library python also has a library called itertoolswhich has really cool efficient solutions to problems.
from itertools import combinations
teams = ["Packers", "49ers", "Ravens", "Patriots"]
for game in combinations(teams, 2):
print game
>>> ('Packers', '49ers')
>>> ('Packers', 'Ravens')
>>> ('Packers', 'Patriots')
>>> ('49ers', 'Ravens')
>>> ('49ers', 'Patriots')
>>> ('Ravens', 'Patriots')
False == True
This is more of a fun one than a useful technique. In python True and False are basically just global variables. Thus:
False = True
if False:
print "Hello"
else:
print "World"
>>> Hello
one more : Useful for working with the interpreter. Underscore uses last result.
>>> 2 + 2
4
>>> _ * 2
8
>>> _ + 1
9
Thanks for reading!