Conditionals and Loops usage is imperative in building a strong foundation for a career that requires one supporting either development or infrastructure operations.

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Unlike curley braces marking the begin and end of blocks on other Languages like C, all the statements inside a block shoud be equally intended, for python to know the beginning and end of a block.

CONDITIONALS

Executes something based on conditions.

if
create variables for two persons with their roll number and age.

 person_number1 = 10
 person_number2 = 17
 person_number1_age = 60
 person_number2_age = 40

call out person-1 , if he has the smaller roll number

 if (person_number1 < person_number2):
     print "call out person-1 "

call out person-1 

if..else
call out the person that has the smaller roll number.

 if (person_number1 < person_number2):
     print "call out person-1 "
 else:
     print "call out person-2"

call out person-1 

if..elif..else
Call out the person that has the smaller roll number.
Also, Check if they have the same roll numbers

 if (person_number1 < person_number2):
     print "call out person-1 "
     elif (person_number2 > person_number1):
	         print "call out person-2"
     else:
	         print "They both have the same number!?"

call out person-2

Nested if..else
Create variables, but with same roll number for both.

person_number1 = 10
person_number2 = 10
person_number1_age = 60
person_number2_age = 40

Call out the person that has the smaller roll number.
Check if they have the same roll numbers
If they do, call out the elderly person first

 if (person_number1 < person_number2):
          print "call out person-1 "
     elif (person_number2 < person_number1):
	         print "call out person-2"
     else:
	         print "They both have the same number! ?"
	         print "Call out the elderly first"
	         if (person_number1_age > person_number1_age):
		          print "call out person-1 , he is the elder one"
	         else:
		          print "call out person-2, he is the elder one"

call out person-2, he is the elder one

Conditionals would do just fine as long as the number of variables are limited.
Assuming a large number of variables, it would only make sense to use a looping mechanism to loop through the list.

LOOPS

for loop
In an array called ‘arr’ containing people’s ages, remove the ones that are under 18.

 arr=[33, 11, 19, 12, 99, 24, 88, 67]
 for age in arr:
     if (age<18):  #check if the age number is less than 18
             print "under age!"
             position=arr.index(age) #get the index position of number in array
             arr.pop(position)       #remove the number

under age!
11
under age!
12

print arr #print the array again.

[33, 19, 99, 24, 88, 67]

while loop
Call the oldest person out first, by looking at an array of their ages.

 while ( len(a) != 0 ):        #Do the below items while array is not empty.
     smallest=a.index(max(a))  #Gets the position of the element that has the smallest value in an array
     a.pop(smallest)           #Removes the element with smallest value
     print a                   #print the array

99
[33, 19, 24, 88, 67]
88
[33, 19, 24, 67]
67
[33, 19, 24]
33
[19, 24]
24
[19]
19
[]

break
break stops execution and exits the loop.
Let’s Create a array called basket with differents fruits as array elements.

 basket = ["apples","mangos","bananas","oranges","coconuts"]
 for fruit in basket:
     print "checking item", fruit
     if (fruit == "apples"):
         print ("apples found")

checking item apples
apples found
checking item mangos
checking item bananas
checking item oranges
checking item coconuts

In the above example, we could see that even after apples are found, the iteration continues.
break is useful when we are sure when to stop the loop from going further.

 for fruit in basket:
     print "checking item", fruit
     if (fruit == "apples"):
         print ("apples found")
         break

checking item apples
apples found

In the above example, since we know there is an occurance of apples only once, we break when its found.

continue
continue on the other hand continues to the next iteration of the loop and if placed conditionally, it would not execute the statements inside the block if the condition is met.

 for i in basket:
     if (i == "bananas"):
       continue
     print "checking out",i

checking out apples
checking out mangos
checking out oranges
checking out coconuts

Python basics: Functions: NEXT →

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