INFS1101 Python Basic Syntax

Python code general guidelines

• Write one instruction per line

• Indentation

Comment

• Serve the purpose of offering explanations to the source code reader regarding the actions taking place within a specific code block where the comment is placed

• When the code is executed, the interpreter disregards comments.

• A single-line comment is initiated with the pound sign (#).

Indentation

It is of utmost importance as it indicates blocks of coded 

Print Function

print (“Hello“, “World“)

Variables

they are defined and assigned whenever needed

• The assignment is using the = sign

letter or underscore

Every variable should start by a ____________, that can be followed by any series of letters, digits, or underscores.

reserved words

You cannot use _______ as variable names / identifiers.

- ex. if=40

True 

Variables in python are case-sensitive to letter case. 'myVariable' and 'myvariable' are seen as different variables.

int

integer numbers

the syntax /

•the result is the quotient which is a float

the syntax //

•the result is the quotient which is an integer

Float

floating-point numbers (decimal)

3.0

What does float(3) returns ?

Error

What does int("3.2") return ?

-2

What does int(-2.7) return ?

String

By default, in Python, the input function reads the user's input as a ______.

name=input("What is your name?")

output is saved in a variable, function name, one argument

int

We can convert the string output of the input function into an integer using the built-in ______ function

float

We can convert the string output of the input function into a float using the built-in ______ function

False

In Python, the code inside an f-string is not executed before it's printed.

Variable type - String

a list of characters, where each character is a letter, a digit or other symbols

String length

The number of characters in a string

greeting = HELLO

greeting[-1]

O

H

greeting = HELLO

greeting[0]

greeting[0:5]

greeting = "HELLO WORLD"

displays: 'HELLO'

displays: 'HELLO W'

greeting = "HELLO WORLD"

greeting[:7]

.upper()

converts a string to uppercase

.lower()

converts a string to lowercase

.capitalize()

converts the first letter of the string to uppercase

Decision in Python – Simple if Statement

if (condition):

instruction1_inside_if

instruction2_inside_if

instruction_outside_if

• Colon (:) → required at the end of the condition

• No then keyword → it is implicit

• Indentation → determines what belongs inside the if block

• Inside the if → instructions run only if the condition is true

• Outside the if → runs regardless of condition outcome

• Brackets around condition: optional if simple, good practice if complex

By indentation

How does Python know which instructions belong inside the if block?

Only if the condition is true

When are the instructions inside the if block executed?

No, else has no condition.

If-Else Statement

Is there a condition after else in Python?

The if block executes, then the instruction outside the if. The else block is skipped.

If-Else Statement
What happens if the condition is true?

The if block is skipped, the else block executes, then the instruction outside the if.

If-Else Statement

What happens if the condition is false?

When condition1 is false and condition2 is true.

if-elif-else statement
When is the elif block executed?

When all previous conditions are false.

if-elif-else statement

When is the else block executed?

Exactly one block.

if-elif-else statement
In an if-elif-else chain, how many blocks are executed?

Boolean operators

helps you make decisions with True and False. 'and' needs both to be True, 'or' needs at least one, and 'not' flips them around.

and Operator

• Meaning: Both conditions must be True → result True

• False if either condition is False

• Example:

x = 5
y = 10
if x > 0 and y > 5:
    print("Both conditions are True")
else:
    print("At least one condition is False")

and → all must be True

or Operator

• Meaning: At least one condition must be True → result True

• False only if both conditions are False

• Example:

x = 5
y = 2
if x > 0 or y > 5:
    print("At least one condition is True")
else:
    print("Both conditions are False")

or → at least one True

len(variable)

to get the length of the characters

{ } curly brackets

If you want to add a variable in an f string, what do we put?