Python Control Flow

Overview

In this lesson, we'll be learning and implementing python control flow, and proper indentation.

Getting Started

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If/Else/ElIf

In python, we can perform logic utilizing if, elif, and else statements to check a condition. Each statement creates a block, and each block must be indented correctly or our code will fail to run. Whatever is declared inside of this block is only accessible within that scope. Common indentation in python is typically 1 tab or 2 spaces, here's an example:

if 5 > 2:
    print('Yay')
elif 5 > 3:
    print('Ohhh')
else:
    print('Whoops')

Notice the syntax, in Python we use the : symbol to indicate the end of our condition. The code after is indented to declare a block or scope.

Here's a comparison between javascript if's and python if's:

Javascript	Python
if(something){}	if something:
else if (something){}	elif something:
else {}	else:

As you can see they're quite similar, but syntactically different.

and's not's and Everything Else

Python also has comparison operators such as < and >. Here's a list of python's comparison and logical operators with their js counterparts:

Javascript	Python	Operation
!==	!=	Not Equal
===	==	Equals
>	>	Greater Than
<	<	Less Than
>=	>=	Greater Than Or Equal
<=	<=	Less Than Or Equal
!	not	Logical Not
&&	and	Logical And
||	or	Logical Or

Ternary Operators

Just like with JavaScript, python also has an option for creating ternary statements. Ternaries can be useful if you'd like a more concise method for writing conditional statements that only have 2 possible outputs for a certain expression.

With JavaScript, our ternary statements look like this:

(someExpression) ? case1 : case2;

In python, ternaries are somewhat more legible. They are written by putting our cases to be output on both sides of an expression wrapped in an if/else. Example:

value_if_true if some_expression else value_if_false
# The left side executes if the expression evaluates to True
# The right side executes if the expression evaluates to False

You Do

Utilizing the above table, work in the check_gpa function in main.py and follow the instructions.

Run the test_gpa.py file to test your logic: python3 test_gpa.py. If everything is correct you'll have an ok message printed to your terminal.

Recap

In this lesson we learned about control flow statements in Python 3 along with realizing how important indentation can be for them to work properly. A few key concepts to note:

• Python conditional statements are typically written in blocks of code following a colon :
• Instead of writing else if() like we would in JavaScript, in Python it is written as elif
• Logical operators like &&,!,|| in JavaScript are written more semantically in Python: and,not,or
• Ternary statements can be written in Python by writing a conditional expression between an if/else with cases on each side for a True/False output of the expression

Resources

• Python If Else
• Python Ternary Operators