Table of Contents
Since we have seen that control structure depends on ==test==. Test is nothing but a statement in pyton whose value is either
False but not together. For this we have a data type in python to represent this, known as boolean data type.
Assigning Boolean Data
test1 = True test2 = False print(test1) print(test2)
Many relational operation result in boolean in pyton. For example if we ask following questions?
test1 = 5 >= 0 # True test2 = 5 < 0 # False test3 = 6 == 3 # False test4 = (6/2 == 3) # Ture, use bracket for better looks print(test1) print(test2) print(test3) print(test4)
True False False True
We can also check some variable has a particular value or not using this idea.
f_name = "Sandeep" l_name = "Suman" full_name = f_name + " " + l_name test1 = (full_name == "Sandeep Suman") print(test1)
Boolean data has three main operation. Others are combination of them
- not: It interchange the value of boolean between
- or: It takes the logical
oroperation between two boolean statements.
- and: It takes the logical
andoperation between two boolean statements.
The result can be summarized in a table as follows
|A||B||not A||not B||A == B||A =! B||A or B||A and B|
f_name = "Sandeep" l_name = "Suman" full_name = f_name + " " + l_name test1 = (full_name == "Sandeep Suman") # True test2 = not test1 # not True = False test3 = (full_name == "Sandeep Suman") or (5 <= 0) # True OR False = True test4 = (full_name == "Sandeep Suman") and (5 <= 0) # True AND False = False print(test1) print(test2) print(test3) print(test4)
True False True False
Till now all the lines of a program run one by one. The control structure will enable us to run a line based on a ==test==.
The structure of general control struructure in python(or in any programming language) will look like the following:
if <test1>: <statement1> elif <test2>: <statement2> . . . else: <final statement>
The situation can graphically represented as the following diagram
If we look at another perspective we can think this as the following sequnce of tests
When the i-th test fails, then program check for (i+1)-th test and so on. If any test say k-th one will pass then the program will run the k-th statement will run and program will exit this control structure. If all the statement fails the program will run the final statement nested under
Except the first if statement all other are optional. We can combine as many test as we want.
One Test: The smallest possible program with
ifstatement can written as following
number = 77 if number > 60: # colon represent a block in python print("1st Devision") # each block need to be indented by 4 whitespace
The output is expected. But even if the number $\leq 60$, we will not get any output because the code has no
number = 55 if number > 60: print("1st Division")
If…else: We can combine
elseto catch the program when test fails as follows
number = 55 if number > 60: print("1st Division") else: print("Not 1st Division")
Not 1st Division
Elif: More than one test can be used using
number = 37 if number >= 60: print("1st Division") elif number >= 45: print("2nd Division") elif number >= 35: print("Third Division") else: print("Fail")
Ex: Change the number to get each type of output.
Ex: Write a program that will give the grade of a student based on marks. You can use any criteria for grade.