COMP7004 - Systems Scripting
Lecture 10: Python Basics
Dr. Vincent Emeakaroha
vincent.emeakaroha@mtu.ie
Semester 2, 2026
Lecture Goals
• Introduction to Python scripting language
• Keywords
• Expressions
• Operators
• Python syntax and basic structures
• Data types
• First Python program
History
• Python was first released in 1991
• Although work on it started in 1980s
• Created by Guido Van Rossum
• Dutch programmer
• Name “Python” does not come from the dangerous snake
• Derived from comedy series “Monty Python's Flying Circus”
• Latest stable version is 3.14.3
• Released in February 2026
• https://www.python.org/downloads/
Features
• Easy to learn
• Simple language with easier syntax to read and write
• Portability
• Have support across variety of operating systems
• Write on one platform and run in another without issues
• Extensible
• Can be easily combined with other programming languages to extend
capabilities
• High-level scripting language
• In-built memory management and garbage collection
• Large standard library collection
• Increases efficiency by avoiding repeating of existing code
Background
• By installing the Python interpreter and Python Virtual Machine…
• Computer able to understand the Python language and to perform some
computations based on its Python knowledge.
Key Concepts
• After installing Python Runtime, what knowledge does
a computer have?
Three knowledge levels:
1. Default knowledge → Prelude.
2. Linked knowledge → Imported.
3. New knowledge → Generated.
Default Knowledge -> Prelude
• Let’s suppose a computer speaks Python. Thus, the computer has some
implicit knowledge of Python’s grammar and expressions:
• Keywords: It knows what is a for loop, if statement…
• Datatypes: It knows that 5 is an integer, that True is a Boolean…
• Operators: It knows that 5 < 6 = True, that True /\ False = False…
• It understands functions and modularity: It has a value/reference
parameter passing policy, strictness/laziness of parameter evaluation…
• This is usually referred to as the programming language
prelude. By speaking Python, the computer understands all
these things (it is part of its knowledge) and thus can do
computations using them.
Linked Knowledge -> Imported
• A computer can borrow some knowledge generated by others:
• E.g., the Python prelude does not include logarithmic operations. Thus, it is
not part of the default knowledge a computer has, so it cannot do
computations including logarithms.
• However, this can be fixed by borrowing the external library:
import math;
• This extends the Python knowledge the computer has with
logarithms and other maths operations, which can be from now on
part of the operations the computer can do.
New Knowledge -> Generated
• We can extend by ourselves (via Python programs) the Python
knowledge a computer can use.
• Imagine we want to compute the number of words written in a
text file.
• This functionality does not belong to the Python prelude, so
the computer does not know how to do it just by the sake of
speaking Python.
• Moreover, let’s suppose that nobody in the Python community
did this before (of course this is not the case, but let’s suppose
it is). Thus, the computer cannot borrow this knowledge by
importing it neither.
New Knowledge -> Generated
• We can extend the knowledge of Python by making it to
open a text file and count the words written on it. All we
need is to:
1. Create a new Python program (e.g., myProgram.py).
2. Implement by ourselves within the program a new function (e.g.,
myCountWords) achieving the functionality required:
def myCountWords(file):
#function content (based on knowledge the computer has)
3. Import the program myProgram.py, so that the computer learns all
the new functions defined on it.
4. Now the computer can use myCountWords as part of its Python
knowledge.
Python Programming Basics
• Since the three categories of knowledge have been introduced,
let us elaborate a bit more on each of them as follows:
Default knowledge (Prelude):
Keywords, Data Types, Operators
Linked knowledge (Imported):
Imports
New knowledge (Generated):
Variables, Functions
and, for the sake of being used for new generated knowledge:
Control Flow, Exception Handling, User Inputs
Keywords
• A keyword, or reserved word, is a word that is reserved by a program
because it has a special meaning.
• This keyword and its meaning is known by the computer, as is part of
the Prelude or default knowledge.
• The Python language has a small subset of keywords:
Interactive Shell: Entry into Python
• Lunching Python interactive shell, e.g.,
• Windows: All Programs -> Python 3.13 -> IDLE
• Mac OS X: Applications -> Python 3.13 -> IDLE
• Linux (Ubuntu): Open terminal window and enter idle or idle3
• When Python shell is lunched
• A prompt “>>>” will appear
• You are ready to let Python do something for you
• A simple math with Python
• Example: >>> 4+4
• Output: 8
Expression
• An expression is the most basic programming instruction
• Example: 4+4
• Expressions consist of
• Values such as 4
• Operators such as +
• They can evaluate down to a single value
• Meaning one can use expression anywhere in Python where
single value is required
• A single value without operator is also an expression but it
evaluates to itself.
Operators
Operators Operation Example Evaluates to …..
**
Exponent
2 ** 3
8
%
Modulus/Remainder
22 % 8
6
//
Integer division/floored quotient
22 // 8
2
/
Division
22
/ 8
2.75
*
Multiplication
3 * 5
15
-
Subtraction
5
- 2
3
+
Addition
4 + 4
8
Operator Precedence
• Order of operator execution
• Same to that of Mathematics
• **, *, /, //, %, + and -, from left to right priority
• Examples on Python shell:
• >>> 2 + 3 * 6
• Output: 20
• >>> (2 + 3) * 6
• Output: 30
Expression and Error
• The rule for putting value and operator together to form
expression is fundamental to Python programming language.
• Just like grammar rules help us to communicate
• In case of wrong/bad expression
• Python outputs syntax error message
• Example:
>>> 5 +
SyntaxError: invalid syntax
• One can always check if an expression works by typing it into
the Python interactive shell.
Data Types
• Specifies a category for values
• Every value belongs to exactly one data type
• Three basic data types in Python
• Integer or int: indicate values that are whole numbers
• Floating-point numbers or floats: indicate numbers with
decimal points
• Strings: indicates text values. Always surround strings in a
single or double quotes
• Python is a typeless language. This means that you do not
have to declare the variable type. The assigned value
determines the type for the variable.
Common Data Types
Data Type
Example
Integers
-
2, -1, 0, 1, 2, 3, 24, 456
Floating
-point numbers
-
1.25, -1.0, 0.0, 0.5, 1.6, 42.586
Strings
’a’, ‘aa’, ‘hello’, ‘22 dogs’, ‘big 5’
• You can have strings with no character
• Called “blank string”
• Example: ‘ ‘ or “ “
• More on strings later in the lecture
Storing Values in Variables
• A variable is like a named box in a computer memory where
one can store a single value.
• Expression results can be stored in variables for later usage.
• Variable names
• Can be chosen by the programmer considering language restrictions.
• Names should be self descriptive for ease of understanding.
• Assignment statement
• Enable storing values in variables.
• Consist of a variable name, an equal sign and the value to be stored.
• Example: counter = 40
• Means that the variable “counter” will have the integer value 40 stored in it.
Interactive Shell: Variable Example
>>> counter = 40
>>> counter
40
>>> nums = 7
>>> counter + nums
47
>>> counter + nums + counter
87
>>> counter = counter + 5
>>> counter
45
Variable Naming Convention
• Variables can be named anything as long as they obey
these three rules:
1. It can be only one word.
2. It can use only letters, numbers, and the underscore
(_) character.
3. It cannot begin with a number.
Valid and Invalid Variable Names
Valid Variable Names Invalid Variable Names
balance
current
-balance (Hyphens not allowed)
currentBalance
current balance (Spaces not allowed)
current_balance
4account (Cannot begin with a number)
_counter
42 (Cannot begin
with a number)
COUNTER
total_$um
(Special characters like $ are not allowed)
account4
’hello’ (Special characters like ‘ are not allowed)
• Variable names are case sensitive
• COUNTER, counter, Counter, and couNter are four different variables.
• Python has the convention to start variable names with a lowercase letter
• Prefer usage of camelcase instead of underscores
• Example: lookLikeThis instead of look_like_this. Note that both are valid variable names
Writing First Program
• Requires a text editor
• Stores the Python code in a file
• Run file to execute program
• IDLE platform
• Select File -> New File
• Start typing your code and save afterwards (File -> Save
As)
• To run the program
• Select Run -> Run Module or press F5
first.py
1) # This program says Hello and ask for my name
2) print('Hello World!')
print('What is your name?')
3) myName = input()
print('It is good to meet you ' + myName)
print('The length of your name is: ')
4) print(len(myName))
print('What is your age?')
myAge = input()
5) print('You will be '+ str(int(myAge)+1) + ' in a year.')
Comments
• Python ignores comments
• Useful for writing notes and documenting code
• Starts with a harsh mark ”#”
1) # This program says Hello and ask for my name
• Blank lines are also ignored by Python
• Useful for organising codes in paragraphs
• Easy reading like in a book
The print() Function
• Outputs content on the screen
2) print('Hello World!')
print('What is your name?')
• The line “print(‘Hello World!’)” means print out the text in the
string ‘Hello World!’
• The value ‘Hello World!’ is being passed to the function print().
• The value passed to a function is known as “argument”.
• More details on functions follows in later lectures.
The input() Function
• Reads in user inputs from the keyboard (standard
input)
• Waits until user types in some text.
3) myName = input()
• Evaluates the user text as string and assigns the value
to the variable “myName”.
The len() Function
• Accepts a string argument
• Returns the number of characters in that string as integer value.
print('The length of your name is: ')
4) print(len(myName))
• “len(myName)” evaluates to an integer value and this value is
passed to the print function to output it on the screen.
• Note that the print function accepts both integer and string
arguments
• Implicit concatenation of both leads to an error.
Concatenation of Integer and String
• Interactive shell example:
>>> print('I am ' + 26 + ’ years old')
Traceback (most recent call last):
File "<pyshell#13>", line 1, in <module>
print('I am ' + 26 + ’ years old')
TypeError: must be str, not int
• This error is not caused by the print function but by the
expression
• ‘I am’ + 26 + ‘years old’
• Addition of string and integer value not allowed
• This can be fixed by using a string version of integer instead
The str(), int() and float() Functions
• str() converts an integer value to a string version
• Example: >>> str(29) will output ‘29’
• >>> print('I am ' + str(26) + ' years old')
• ' I am 26 years old '
• int() converts a string version of integer to integer
• Example: >>> int('26') will output 26
• float() converts a string version of floating-point number to
float
• Example: >>> float(' 4.16 ') will output 4.16
Concatenation: first.py
• The function “input()” always returns a string value:
myAge = input()
5) print('You will be '+ str(int(myAge)+1) + ' in a year.’)
• In the above extract, the functions int() and str() are used
to get the appropriate data types to avoid syntax error.
Thank You!
