Python Shortcuts for the Python Beginner (Posted on January 26th, 2013)

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.

Swapping Variables

  1. x = 6
  2. y = 5
  3.  
  4. x, y = y, x
  5.  
  6. print x
  7. >>> 5
  8. print y
  9. >>> 6

Inline if Statement

  1. print "Hello" if True else "World"
  2. >>> Hello

Concatenations

The last one is a pretty cool way to combine objects of two different types.

  1. nfc = ["Packers", "49ers"]
  2. afc = ["Ravens", "Patriots"]
  3. print nfc + afc
  4. >>> ['Packers', '49ers', 'Ravens', 'Patriots']
  5.  
  6. print str(1) + " world"
  7. >>> 1 world
  8.  
  9. print `1` + " world"
  10. >>> 1 world
  11.  
  12. print 1, "world"
  13. >>> 1 world
  14. print nfc, 1
  15. >>> ['Packers', '49ers'] 1

Number Tricks

  1. #Floor Division (rounds down)
  2. print 5.0//2
  3. >>> 2
  4.  
  5. #2 raised to the 5th power
  6. print 2**5
  7. >> 32

Be careful with division and floating point numbers.

  1. print .3/.1
  2. >>> 2.9999999999999996
  3.  
  4. print .3//.1
  5. >>> 2.0

Numerical Comparison

This is a pretty cool shortcut that I haven't seen in too many languages.

  1. x = 2
  2.  
  3. if 3 > x > 1:
  4.     print x
  5. >>> 2
  6.  
  7. if 1 < x > 0:
  8.     print x
  9. >>> 2

Iterate Through Two Lists at the Same Time

  1. nfc = ["Packers", "49ers"]
  2. afc = ["Ravens", "Patriots"]
  3.  
  4. for teama, teamb in zip(nfc, afc):
  5.     print teama + " vs. " + teamb
  6.  
  7. >>> Packers vs. Ravens
  8. >>> 49ers vs. Patriots

Iterate Through List With an Index

  1. teams = ["Packers", "49ers", "Ravens", "Patriots"]
  2. for index, team in enumerate(teams):
  3.     print index, team
  4.  
  5. >>> 0 Packers
  6. >>> 1 49ers
  7. >>> 2 Ravens
  8. >>> 3 Patriots

List Comprehension

With a list comprehension we can turn this:

  1. numbers = [1,2,3,4,5,6]
  2. even = []
  3. for number in numbers:
  4.     if number%2 == 0:
  5.         even.append(number)

Into this:

  1. numbers = [1,2,3,4,5,6]
  2. 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:

  1. teams = ["Packers", "49ers", "Ravens", "Patriots"]
  2. print {key: value for value, key in enumerate(teams)}
  3. >>> {'49ers': 1, 'Ravens': 2, 'Patriots': 3, 'Packers': 0}

Initialize List Values

  1. items = [0]*3
  2. print items
  3. >>> [0,0,0]

Converting a List to a String

  1. teams = ["Packers", "49ers", "Ravens", "Patriots"]
  2. print ", ".join(teams)
  3. >>> '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:

  1. data = {'user': 1, 'name': 'Max', 'three': 4}
  2. try:
  3.     is_admin = data['admin']
  4. except KeyError:
  5.     is_admin = False

Do this:

  1. data = {'user': 1, 'name': 'Max', 'three': 4}
  2. 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.

  1. x = [1,2,3,4,5,6]
  2.  
  3. #First 3 
  4. print x[:3]
  5. >>> [1,2,3]
  6.  
  7. #Middle 4
  8. print x[1:5]
  9. >>> [2,3,4,5]
  10.  
  11. #Last 3
  12. print x[-3:]
  13. >>> [4,5,6]
  14.  
  15. #Odd numbers
  16. print x[::2]
  17. >>> [1,3,5]
  18.  
  19. #Even numbers
  20. print x[1::2]
  21. >>> [2,4,6]

FizzBuzz in 60 Characters

A while back Jeff Atwood popularized a simple programming exercise called FizzBuzz. Here is the excerpt on the problem:

Write a program that prints the numbers from 1 to 100. But for multiples of three print "Fizz" instead of the number and for the multiples of five print "Buzz". For numbers which are multiples of both three and five print "FizzBuzz".

Here's a short, fun way to solve the problem.

  1. 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. I find the Counter to be quite useful on occasion. Some of you may even find it useful if you're participating in this year's Facebook HackerCup.

  1. from collections import Counter
  2.  
  3. print Counter("hello")
  4. >>> Counter({'l': 2, 'h': 1, 'e': 1, 'o': 1})

Itertools

Along with the collections library python also has a library called itertools which has really cool efficient solutions to problems. One is finding all combinations. This will tell us all the different ways the teams can play each other.

  1. from itertools import combinations
  2.  
  3. teams = ["Packers", "49ers", "Ravens", "Patriots"]
  4. for game in combinations(teams, 2):
  5.     print game
  6.  
  7. >>> ('Packers', '49ers')
  8. >>> ('Packers', 'Ravens')
  9. >>> ('Packers', 'Patriots')
  10. >>> ('49ers', 'Ravens')
  11. >>> ('49ers', 'Patriots')
  12. >>> ('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:

  1. False = True
  2. if False:
  3.     print "Hello"
  4. else:
  5.     print "World"
  6.  
  7. >>> Hello

If you've got any other cool tips/tricks leave them in the comments below. Thanks for reading!

Tags: Python