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Python | Set 4 (Dictionary, Keywords in Python)
  • Difficulty Level : Medium
  • Last Updated : 24 Jul, 2018

In the previous two articles (Set 2 and Set 3), we discussed the basics of python. In this article, we will learn more about python and feel the power of python.
Dictionary in Python
In python, dictionary is similar to hash or maps in other languages. It consists of key value pairs. The value can be accessed by unique key in the dictionary.

# Create a new dictionary 
d = dict() # or d = {}
# Add a key - value pairs to dictionary
d['xyz'] = 123
d['abc'] = 345
# print the whole dictionary
print d
# print only the keys
print d.keys()
# print only values
print d.values()
# iterate over dictionary 
for i in d :
    print "%s  %d" %(i, d[i])
# another method of iteration
for index, key in enumerate(d):
    print index, key, d[key]
# check if key exist
print 'xyz' in d
# delete the key-value pair
del d['xyz']
# check again 
print "xyz" in d


{'xyz': 123, 'abc': 345}
['xyz', 'abc']
[123, 345]
xyz 123
abc 345
0 xyz 123
1 abc 345

break, continue, pass in Python
break – takes you out of the current loop.
continue – ends the current iteration in the loop and moves to the next iteration.
pass – The pass statement does nothing. It can be used when a statement is required. syntactically but the program requires no action. It is commonly used for creating minimal classes.

# Function to illustrate break in loop
def breakTest(arr):
    for i in arr:
        if i == 5:
        print i,
    # For new line
# Function to illustrate continue in loop
def continueTest(arr):
    for i in arr:
        if i == 5:
        print i,
    # For new line
# Function to illustrate pass 
def passTest(arr):
# Driver program to test above functions
# Array to be used for above functions:
arr = [1, 3 , 4, 5, 6 , 7]
# Illustrate break
print "Break method output"
# Illustrate continue 
print "Continue method output"
# Illustrate pass- Does nothing


Break method output
1 3 4
Continue method output
1 3 4 6 7

map, filter, lambda
map – The map() function applies a function to every member of iterable and returns the result. If there are multiple arguments, map() returns a list consisting of tuples containing the corresponding items from all iterables.
filter – It takes a function returning True or False and applies it to a sequence, returning a list of only those members of the sequence for which the function returned True.
lambda- Python provides the ability to create a simple (no statements allowed internally) anonymous inline function called lambda function. Using lambda and map you can have two for loops in one line.

# Python program to test map, filter and lambda
# Function to test map 
def cube(x):
    return x**2
# Driver to test above function
# Program for working of map 
cubes = map(cube, range(10))
print cubes
# first parentheses contains a lambda form, that is  
# a squaring function and second parentheses represents
# calling lambda
print (lambda x: x**2)(5)
# Make function of two arguments that return their product
print (lambda x, y: x*y)(3, 4)
special_cubes = filter(lambda x: x > 9 and x < 60, cubes)
print special_cubes


[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
[16, 25, 36, 49]

For more clarity about map, filter and lambda, you can have a look at the below example:

#code without using map, filter and lambda
# Find the number which are odd in the list
# and multiply them by 5 and create a new list
# Declare a new list
x = [2, 3, 4, 5, 6]
# Empty list for answer
y = []
# Perform the operations and print the answer
for v in x:
    if v % 2:
        y += [v*5]
print y


[15, 25]

The same operation can be performed in two lines using map, filter and lambda as :

#above code with map, filter and lambda
# Declare a list 
x = [2, 3, 4, 5, 6]
# Perform the same operation as  in above post
y = map(lambda v : v * 5, filter(lambda u : u % 2, x))
print y


[15, 25]


References :
This article is contributed by Nikhil Kumar Singh
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

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