for Loop in Python
for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string).
With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc.
for var in sequence: statement(s) must be indented
var is the variable that takes the value of the item inside the sequence on each iteration.
Loop continues until we reach the last item in the sequence.
Example 1:Print each fruit in a fruit list:
fruits = ["apple", "banana", "mango"] for x in fruits: print(x)OUTPUT
apple banana mango
Example 2:Program to find the sum of all numbers stored in a list
# List of numbers numbers = [1,2,3,10,20,34] # variable to store the sum sum = 0 # iterate over the list for var in numbers: sum = sum+var # Output: The sum is 70 print("The sum is", sum)OUTPUT
The sum is 70
Looping through a String
Even strings are iterable objects, they contain a sequence of characters:
Example 3:Loop through the letters in the word "prowess":
for x in "prowess": print(x)OUTPUT
p r o w e s s
The range() function :
We can generate a sequence of numbers using
1. range(stop) always starts from 0 to stop-1.
range(10) will will generate numbers from 0 to 9 (10 numbers).
>>> print(range(10)) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>>
2. range(start, stop, step) We can also define the start, stop and step size.Step size defaults to 1 if not provided.
range(1,10) will will generate numbers from 1 to 9 (10 numbers).
>>> print(range(1,10)) [1, 2, 3, 4, 5, 6, 7, 8, 9] step is 1 >>> print(range(1,10,2)) [1, 3, 5, 7, 9] step is 2 >>> print(range(10,1,-1)) step is -1 [10, 9, 8, 7, 6, 5, 4, 3, 2] #generate the reverse series
We can use the range() function in for loops to iterate through a sequence of numbers.
>>> for i in range(5): print(i) 0 1 2 3 4
range() function can be combined with the
len() function to iterate though a sequence using indexing.
Program to iterate through a list using indexing fruit = ['apple', 'banana', 'mango'] # iterate over the list using index for i in range(len(fruit)): print("I like", fruit[i])OUTPUT
I like apple I like banana I like mango
for loop with else :
In python, a for loop can have an optional else block as well. The
else block is executed if the items in the sequence used in for loop exhausts.
for x in range(6): print(x) else: print("Finally finished!")OUTPUT
0 1 2 3 4 5 Finally finished!
A nested loop is a loop inside a loop.
The "inner loop" will be executed one time for each iteration of the "outer loop":
Print each adjective for every fruit:
adj = ["red", "big", "tasty"] fruits = ["apple", "banana", "cherry"] for x in adj: for y in fruits: print(x, y)OUTPUT
red apple red banana red cherry big apple big banana big cherry tasty apple tasty banana tasty cherry
Next topic is break, continue and pass statements
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