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Python Basics

Python is a dynamically typed, interpreted language. Python interpreter is written in C-language. Interpreter program reads and performs the Python codes/ instructions. The interpreters interacts with the operating system layer (use network, keyboard, mouse, monitor, hard drive etc.).

Hello Python​

It is customary to write our first program that prints some message in the screen:

print("Hello Python!")

Assigning variables​

a = 5
b = 3
a + b
a * b
a - b
Good to know

Due to how the numbers are stored in computer memory, floating point algebra sometimes might produce unexpected results. Notice the following discrepancy (floating point addition/ subtraction is not associative):

>>> (1.2 + 1E20) - 1E20
0.0
>>> 1.2 + (1E20 - 1E20)
1.2

String concatenation​

greeting = "Hello"
name = "Pranab"
print(greeting + " " + name)

For performance improvement and better readability, consider using join instead of in-place string concatenation.

" ".join([greeting, name])

Loosely typed​

As we have seen, we do not need to define the datatype in python. Interestingly, for certain operations, we can even mix types:

my_str = "Rain! "
my_str * 3  # multiplying a str with int

Input​

Collecting user input:

age = input("How old are you? ")
type(age)
note

Notice that variable assigned from input is a string, even if a number is entered.

Type conversion​

age = int(age)
type(age)

String formatting​

"Singapore".upper()
"Singapore".lower()
"das".capitalize()
"pranab das".title()
"ABCDefgh".swapcase()
name = 'Pranab'
age = 34
print("Name: {0}. Age: {1} years.".format(name, age))

You can also format in the following way:

print("Name: {name}. Age: {age} years.".format(name=name, age=age))

Starting from Python 3.6 and above:

print(f"Name: {name}. Age: {age} years.")