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Trick and tips for better code in python

This notes are base in the Medium post called "five Python tricks you need to learn today" and different articles or answers i found on Internet.

TIp 1: Clean - Powerful One-liners

Conditional statements

A normal If conditional will look like this:

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if alpha > 7 :
    beta = 999
elif alpha == 7:
    beta = 99
else:
    beta = 0

but this can be one line, it can be simplified in this way:

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beta == 999 if alpha > 7 else 99 if alpha == 7 else 0

for loops

for example, doubling a list of integers in four lines:

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lst = [1,3,5]
doubled = []
for num in lst:
    doubled.append(num*2)

and it can be simplify to just one line:

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double = [num * 2 for num in lst]

Tip 2: String Manipulation

Reverse a string

we can use ::-1 to reverse a string, like this:

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a = "ilovemyjob"
print a[::-1]
#bojymevoli

join strings

we can print the result of join different strings, or item of a list together:

let say we have this: 

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str1 = "Totally"
str2 = "Awesome"
lst3 = ["Omg", "You", "Are"]

so we can use join() method to create the outcome:

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print ' '.join(lst3)
#Omg You Are
print ' '.join(lst3)+' '+str1+' '+str2
#Omg You Are Totally Awesome

Tip 3: Replace loops for Map, Filter, and Reduce

In some cases what we want to achieve with the loops can be done by map(), filter(), and reduce(), we need to keep in mine the following:

  • Map: Apply the same set of steps to each item, storing the result.
  • Filter: Apply validation criteria, storing items that evaluate True.
  • Reduce: Return a value that is passed from element to element.

here a simple example, first how it will be done by loops

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numbers = [1,2,3,4,5,6]
odd_numbers = []
squared_odd_numbers = []
total = 0
# filter for odd numbers
for number in numbers:
   if number % 2 == 1:
      odd_numbers.append(number)
# square all odd numbers
for number in odd_numbers:
   squared_odd_numbers.append(number * number)
# calculate total
for number in squared_odd_numbers:
   total += number
# calculate average

now let's do it with the functions

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from functools import reduce
numbers = [1,2,3,4,5,6]
odd_numbers = filter(lambda n: n % 2 == 1, numbers)
squared_odd_numbers = map(lambda n: n * n, odd_numbers)
total = reduce(lambda acc, n: acc + n, squared_odd_numbers)
Few things to keep in mine:

  • map() and filter() are native available, but reduce() is part of the library functools.
  • The lambda expression is the first argument, and the second is an iterable.
  • The lambda expression for reduce() requires two arguments: the accumulator (the value that is passed to each element) and the individual element itself.