Python Introduction

Python was created by Guido van Rossum and released in 1991. It was designed to be readable: code looks almost like English, and there is usually one obvious way to do something. Today Python is the language of data science, machine learning, automation, web back-ends, scripting and competitive programming.

print("Hello, Python!")
print("2 + 3 =", 2 + 3)
print("Python" * 3)

Hello, Python!
2 + 3 = 5
PythonPythonPython

Compare that with C: no #include, no main, no semicolons, no types to declare. The program simply runs from top to bottom.

#How Python runs your code

C is compiled ahead of time into machine code. Python is interpreted: the python program reads your .py file, compiles it to bytecode, and the Python virtual machine executes that bytecode line by line.

python3 hello.py          # run a file
python3                   # start the interactive shell (REPL)

In the interactive shell, each line runs as soon as you press Enter — great for experiments:

>>> 7 * 6
42
>>> "kalvium".upper()
'KALVIUM'

#Indentation is syntax

Python uses indentation (4 spaces by convention) to mark blocks. Wrong indentation is an error, not just bad style.

marks = 82
if marks >= 40:
    print("Pass")          # inside the if block
    print("Well done!")
print("Result printed")    # back outside the block

Pass
Well done!
Result printed

#Comments

# A single-line comment starts with a hash.

"""
A string on its own line is often used as a
multi-line comment or documentation (a docstring).
"""

#print() in detail

print("A", "B", "C")                 # separated by spaces
print("A", "B", "C", sep="-")        # custom separator
print("no newline", end=" ... ")     # custom ending
print("continued")
name, score = "Asha", 93.456
print(f"{name} scored {score:.1f}%")  # f-string with formatting
print("Tab\tand\nnewline")

A B C
A-B-C
no newline ... continued
Asha scored 93.5%
Tab	and
newline

f"..." strings (f-strings) put expressions inside { }. They are the modern way to format output and you will use them constantly.

#Python is everywhere