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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.
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python - Sample - python code :
# 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, value in enumerate(d):
print index, value , d[value]
# check if key exist
print 'xyz' in d
# delete the key-value pair
del d['xyz']
# check again
print "xyz" in d
python tutorial - Output :
{'xyz': 123, 'abc': 345} ['xyz', 'abc'] [123, 345] xyz 123 abc 345 0 xyz 123 1 abc 345 True False
![Python - creating dictionary](https://wikitechy.com/tutorials/python/img/python-images/dictionary/creating-dictionary.png)
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.
python - Sample - python code :
# Function to illustrate break in loop
def breakTest(arr):
for i in arr:
if i == 5:
break
print i,
# For new line
print
# Function to illustrate continue in loop
def continueTest(arr):
for i in arr:
if i == 5:
continue
print i,
# For new line
print
# Function to illustrate pass
def passTest(arr):
pass
# 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"
breakTest(arr)
# Illustrate continue
print "Continue method output"
continueTest(arr)
# Illustrate pass- Does nothing
passTest(arr)
python tutorial - Output :
Break method output 1 3 4 Continue method output 1 3 4 6 7
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.
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python - Sample - python code :
# 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
print "MAP EXAMPLES"
cubes = map(cube, range(10))
print cubes
print "LAMBDA EXAMPLES"
# 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)
print "FILTER EXAMPLE"
special_cubes = filter(lambda x: x > 9 and x < 60, cubes)
print special_cubes
python tutorial - Output :
MAP EXAMPLES [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] LAMBDA EXAMPLES 25 12 FILTER EXAMPLE [16, 25, 36, 49]
For more clarity about map, filter and lambda, you can have a look at the below example:
python - Sample - python code :
#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
python tutorial - Output :
[15, 25]
The same operation can be performed in two lines using map, filter and lambda as :
python - Sample - python code :
#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
python tutorial - Output :
[15, 25]