Python Fundamentals: A Beginner’s Guide (Part 1)

1. Virtual Environment

A virtual environment is a feature in Python that allows you to install the same package with different versions on the same system. This enables you to work on multiple projects using different versions of the same package.

1.1. Installing `venv`

The venv module is included in the Python standard library, so you don’t need to install it separately. However, if you are using an older version of Python (before 3.3), you can install virtualenv using pip:

pip install virtualenv

1.2. Creating a Virtual Environment

To create a virtual environment, you can use the venv module, which is included in the Python standard library. Here’s how you can create a virtual environment named myenv:

python -m venv myenv

This command creates a new directory named myenv that contains the necessary files for the virtual environment.

1.3. Activating a Virtual Environment

To activate the virtual environment, you may run the following command:

# For Linux/Mac:
source myenv/bin/activate
# For Windows:
myenv\Scripts\activate

2. Python Packages

2.1. List All the Python Packages

To list or save all the installed packages in the current environment, you can use the following command using freeze:

pip freeze # To list all the installed packages
pip freeze > requirements.txt # To save all the installed packages in a file

2.2. Installing Python Packages

To install a Python package, you can use the pip install command followed by the package name. For example, to install the requests package, you can run:

pip install requests

2.3. Uninstalling Python Packages

To uninstall a Python package, you can use the pip uninstall command followed by the package name. For example, to uninstall the requests package, you can run:

pip uninstall requests

2.4. Run Python Package/Script

To run a python package or script, you can use the following command:

python -m package_name

3. Python Basics

3.1. Running a Python Script

To run a Python script, you can use the following command:

python script.py

3.2. Python Indentation

In Python, the code block (body of the function, loop, etc.) starts with a colon (:) and the line following the colon should be indented.

if 5 > 2:
    print("Five is greater than two!") # Indented block

3.3. Python Comments

There are two types of comments in Python:

# This is a single line comment
""" This is a multiline comment
    This is a multiline comment
    This is a multiline comment
    This is a multiline comment
"""

3.4. Print Statement

The print() function is used to display the output on the console. For example:

print("Hello, World!")

3.5. Data Types

Python has the following data types:

int
float
str
bool
list
tuple
set
dict
None

a = 10 # int
b = 10.5 # float
c = "Hello" # str
d = True # bool
e = [1,2,3] # list
f = (1,2,3) # tuple
g = {1,2,3} # set
h = {"name":"John","age":30} # dict
i = None # None
print(type(a)) # <class 'int'>

Note:Use type() function to check the data type of a variable.As it return the class of the variable.

3.6. Rules of Variable Declaration

A variable name must start with a letter or the underscore character.
A variable name cannot start with a number.
A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ).
Variable names are case-sensitive (age, Age, and AGE are three different variables).

3.7. Type Conversion

You can convert one data type to another using the following functions:

int(): To convert to an integer
float(): To convert to a float
str(): To convert to a string
bool(): To convert to a boolean
list(): To convert to a list
tuple(): To convert to a tuple
set(): To convert to a set
dict(): To convert to a dictionary

a = 10  #a=10
b = float(a) #b=10.0
c = str(a) #c='10'
d = bool(a) #d=True
e = list(c) #e=['1','0']
f = tuple(c) #f=('1','0')
g = set(c) #g={'1','0'}
h = dict(name="John",age=30) or dict([("name","John"),("age",30)]) 
#h={'name':'John','age':30}

Note: Python is dynamically typed, which means a variable’s data type can be changed.

4. Operators

4.1. Arithmetic Operators

+: Addition
-: Subtraction
*: Multiplication
/: Division
%: Modulus
**: Power
//: Floor Division

a = 10
b = 3
print(a + b) # 13
print(a - b) # 7
print(a * b) # 30
print(a / b) # 3.3333333333333335
print(a % b) # 1
print(a ** b) # 1000
print(a // b) # 3

4.2. Assignment Operators

=: Assign value
+=: Add and assign
-=: Subtract and assign
*=: Multiply and assign
/=: Divide and assign
%=: Modulus and assign
**=: Power and assign
//=: Floor Division and assign

a = 10
a += 5 # a = a + 5
a -= 5 # a = a - 5
a *= 5 # a = a * 5
a /= 5 # a = a / 5
a %= 5 # a = a % 5
a **= 5 # a = a ** 5
a //= 5 # a = a // 5

4.3. Comparison Operators

==: Equal to
!=: Not equal to
>: Greater than
<: Less than
>=: Greater than or equal to
<=: Less than or equal to

    a = 10
    b = 20
    print(a == b) # False
    print(a != b) # True
    print(a > b) # False
    print(a < b) # True
    print(a >= b) # False
    print(a <= b) # True

4.4. Logical Operators

and: Returns True if both statements are true
or: Returns True if one of the statements is true
not: Reverse the result, returns False if the result is true

a = 10
b = 20
c = 30
print(a < b and b < c) # True
print(a < b or b > c) # True
print(not(a < b and b < c)) # False

4.5. Identity Operators

is: Returns True if both variables are the same object
is not: Returns True if both variables are not the same object

a = [1,2,3]
b = [1,2,3]
print(a is b) # False
print(a is not b) # True

4.6. Membership Operators

in: Returns True if a sequence with the specified value is present in the object
not in: Returns True if a sequence with the specified value is not present in the object

a = [1,2,3] #Can be used in list , tuple , set , dict, string
print(1 in a) # True
print(4 not in a) # True

4.7. Bitwise Operators

&: AND
|: OR
^: XOR
~: NOT
<<: Left Shift
>>: Right Shift

a = 10
b = 4
print(a & b) # 0
print(a | b) # 14
print(a ^ b) # 14
print(~a) # -11
print(a << 2) # 40
print(a >> 2) # 2

Note: is vs ==

is is used to compare the memory location of two objects.
== is used to compare the values of two objects.

# For Mutable objects (list, dict, set):
a = [1,2,3]
b = [1,2,3]
print(a == b) # True
print(a is b) # False

# For immutable objects (int, float, string, tuple, None):
a = 10
b = 10
print(a == b) # True
print(a is b) # True
c = None
d = None
print(c == d) # True
print(c is d) # True

5.Taking User Input

In Python, you can take user input using the input() function. Here’s an example:

name = input("Enter your name: ")
print("Hello, " + name)

Note: The input() function always returns a string. If you want to convert it to another data type, you can use type conversion functions like int(), float(), etc.

Python Fundamentals: A Beginner’s Guide (Part 1)#

1. Virtual Environment#

1.1. Installing venv#

1.2. Creating a Virtual Environment#

1.3. Activating a Virtual Environment#

2. Python Packages#

2.1. List All the Python Packages#

2.2. Installing Python Packages#

2.3. Uninstalling Python Packages#

2.4. Run Python Package/Script#

3. Python Basics#

3.1. Running a Python Script#

3.2. Python Indentation#

3.3. Python Comments#

3.4. Print Statement#

3.5. Data Types#

3.6. Rules of Variable Declaration#

3.7. Type Conversion#

4. Operators#

4.1. Arithmetic Operators#

4.2. Assignment Operators#

4.3. Comparison Operators#

4.4. Logical Operators#

4.5. Identity Operators#

4.6. Membership Operators#

4.7. Bitwise Operators#

5.Taking User Input#