Python Programming: Useful Tips and Tricks with Short Code Snippets

In this post, we will learn to use some basic tips and tricks of Python.

1. Swap Two Numbers

    >>> x, y = 5, 10
    >>> x, y = y, x
    >>> x
    10
    >>> y
    5
   

2. Reversing String

    >>> x = "hello"
    >>> x[::-1]
    'olleh'
   

3. Sort a list

    >>> a = [5,2,8,3,1]
    >>> sorted(a)
    [1, 2, 3, 5, 8]
    >>> sorted(a,reverse=True)
    [8, 5, 3, 2, 1]
   

4. Reversing a List

    >>> a = [5,2,8,3,1]
    >>> a[::-1]
    [1, 3, 8, 2, 5]
   

5. Split data and assign values to variables

    >>> (age, income) = "35,150000".split(',')
    >>> age
    35
   

6. Access Key and Value from a list using for loop

    mydict = {
        "a":"cat",
        "b":"dog"
    }
   	
    for key,val in mydict.items():
        print("key:", key, "value:", val)
   

7. Access items of two lists of same sizes at the same time

    a = [4,5,6]
    b = [1,2,3]
    for i,j in zip(a,b):
        print(i+j)
    # output
    # 5 7 9
   

8. Create a string from the elements in list and Vice-versa

    mylist = ["hi", "there", "!"]
    string1 = " ".join(mylist)
    string2 = "".join(mylist)
    print(string1)
    print(string2)
    # output
    # hi there !
    # hithere!
   

    newlist = string1.split(" ")
    print(newlist)
    # output
    # ["hi", "there", "!"]
   

9. List comprehension makes the code shorter

   myint = [2,4,6]
   mysquare = []
   for i in myint:
       mysquare.append(i*i)
   print(mysquare)
   # output: [4, 16, 36]
   

   same thing can be done in one line

   myint = [2,4,6]
   mysquare = [i*i for i in myint]
   print(mysquare)
   # output: [4, 16, 36]
   

10. Get arguments from the terminal and put in a list

    import sys
    args = [int(arg) for arg in sys.argv[1:]]
    print(sum(args))
    

    now, save the code in a file (here, test.py) and run like this

    $ python test.py 2 4 6 8
    20
    

11. Single line function using Python Lambda

    # an example function using def
    def testfunc(a,b):
        return a**2 + b**2, a**3 + b**3
    
    x,y = testfunc(2,3)
    print(x,y)
    # output: 13 35
    

    now, let’s create the above function using lambda

    testfunc = lambda a,b: (a**2 + b**2, a**3 + b**3)
    x,y = testfunc(2,3)
    print(x,y)
    # output: 13 35
    

12. map, filter, reduce

    a = [1,2,3,4,5]
    
    square = map(lambda x:x**2, a)
    print(list(square))
    
    even = filter(lambda x:x%2==0, a)
    print(list(even))
    
    from functools import reduce
    summ = reduce(lambda x,y:x+y,a)
    print(summ)
    	
    # output
    # [1, 4, 9, 16, 25]
    # [2, 4]
    # 15 
    

13. Create a dictionary from two lists using dictionary comprehension

    a = [1,2,3,4,5]
    b = ["a", "b", "c", "d", "e"]
    mydict = {i:j for i, j in zip(a,b)}
    print(mydict)
    # output: {1: 'a', 2: 'b', 3: 'c', 4: 'd', 5: 'e'}
    

14. Sort a Dictionary by value

    sorted_dict = {k:v for k,v in sorted(my_dict.items(), key=lambda item: item[1])}
    

15. List edges of a graph using nested comprehension

    G = {
        "a": ["b","c"],
        "b": ["d", "e"],
        "c": ["d", "e"],
        "d": ["e"],
        "e": ["f"]
    }
    
    def edgelist(graph):
        edges = [(key,i) for key,val in graph.items() for i in val]
        return edges
    
    print(edgelist(G))
    # output: [('a', 'b'), ('a', 'c'), ('b', 'd'), ('b', 'e'), ('c', 'd'), ('c', 'e'), ('d', 'e'), ('e', 'f')]
    

16. Flattening a list using itertools

    from itertools import chain
    print(list(chain.from_iterable([[1, 2], [3], [4], [5, 6]])))
    # output: [1, 2, 3, 4, 5, 6]
    

17. use of arguments and keyword arguments in functions

    from functools import reduce
    def mysum(first, second, *args, kw1, **kwargs):
        summ = first + second + reduce(lambda x,y:x+y, [i for i in args]) + kw1 + kwargs["end"]
        return summ
    print(mysum(3, 4, 5, 6, 7, kw1=8, end=10))
    

18. returning function from a function

    def myfunc():
        def new():
            print('hi there!')
        return new
    
    a = myfunc()
    a()
    # output: hi there!
    

19. Use of continue and break in loops

    for i in range(10):
        if (i is 1):
            continue
        if (i > 5):
            break
        print(i)
    # output: 0 2 3 4 5
    

20. Calculate runtime of a function using decorator

    from functools import wraps
    from time import time
    
    def runtime(func):
        @wraps(func)
        def wrapper(*args, **kw):
            start = time()
            result = func(*args, **kw)
            end = time()
            print('runtime: %2.4f sec' %(end-start))
            return result
        return wrapper
    
    @runtime
    def mysum(myrange):
        summ = 0
        for i in range(myrange+1):
            summ += i
        print("sum =", summ)
    
    mysum(5)
    # sum = 15
    # runtime: 0.0002 sec