Loops in Python
Loops in Python
Sometimes we want to repeat a set of statements in our program.
For instance: Print 1 to 1000
Loops make it easy for a programmer to tell the computer, which
set of instructions to repeat, and how!
Types of loops in Python
Primarily there are two types of loops in Python
1.
While loop
2.
For loop
We will look into this one by one!
While loop
The syntax of a while loop looks like this:
''' while condition:
#Body
of the loop '''
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- The block keeps
executing until the condition is true/false
In while loops, the condition is checked first. If it evaluates to
true, the body of the loop is executed, otherwise not!
If the loop is entered, the process of condition check and
execution is continued until the condition becomes false.
Quick Quiz: Write a program to print 1
to 50 using a while loop.
An Example:
i = 0
while i<5:
print(“alok”)
i
= i+1
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(Above program will print Alok 5 times)
Note: if the condition never becomes false, the loop
keeps getting executed.
Quick Quiz: Write a program to print
the content of a list using while loops.
For loop
A for loop is used to iterate through a sequence like a list,
tuple, or string (iterables)
The syntax of a for loop looks like this:
l = [1, 7, 8]
for item in l:
print(item)
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(Above program will print 1, 7, and 8)
Range function in Python
The range function in python is used to generate a sequence of
numbers.
We can also specify the start, stop, and step-size as follows:
range(start, stop, step_size)
- step size is
usually not used with range()
An example demonstrating range() function
for i in range(0, 7): #range(7) can also be
used
print(i) #prints 0 to 6
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For loop with else
An optional else can be used with a for loop if the code is to be
executed when the loop exhausts.
Example:
l = [1, 7, 8]
for item in l:
print(item)
else:
print(“Done”) #This is printed when the
loop exhausts!
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Output:
1
7
8
Done
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The break statement
‘break’ is used to come out of the loop when encountered. It
instructs the program to – Exit the loop now.
Example:
for i in range(0, 80):
print(i) #This will print 0, 1, 2
and 3
if i == 3:
break
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The continue statement
‘continue’ is used to stop the current iteration of the loop and
continue with the next one. It instructs the program to “skip this iteration.”
Example:
for i in range(4):
print(“printing”)
if i == 2: #if i is 2, the iteration
is skipped
continue
print(i)
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pass statement
pass is a null statement in python. It instructs to “Do nothing.”
Example:
l = [1, 7, 8]
for item in l:
pass #without pass, the
program will throw an error
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Chapter 7 – Practice Set
1.
Write a program to print the multiplication table of a given
number using for loop.
2.
Write a program to greet all the person names stored in a list l1
and which starts with S.
l1 = [“alok”, “Sohan”,
“Sachin”, “Rahul”]
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3.
Attempt problem 1 using a while loop.
4.
Write a program to find whether a given number is prime or not.
5.
Write a program to find the sum of first n natural numbers using a
while loop.
6.
Write a program to calculate the factorial of a given number using
for loop.
7.
Write a program to print the following star pattern.
*
***
***** for n=3
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8.
Write a program to print the following star pattern:
*
**
*** for n = 3
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9.
Write a program to print the following star pattern:
* * *
* * #For n=3
* * *
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10. Write a program to print the multiplication table
of n using for loop in reversed order.