Installnig Packages with pip

pip install -i https://pypi.douban.com/simple package_name

Variables and Data Types

Defining Variables

In programming, variables act as containers to store data. For example, when adding two numbers, you first store them in variables and then perform the operation.

value_one = 100
value_two = 87
total = value_one + value_two

Variable Types

Python automatically determines a variable's type based on the assigned value. Use the type() function to check the type.

Identifiers and Keywords

Identifiers

Identifiers are user-defined names for variables, functions, etc. They must start with a letter or underscore and can contain letters, digits, and underscores.

Examples of valid and invalid identifiers:

fromNo12     # Valid
from#12      # Invalid (contains #)
my_Boolean   # Valid
my-Boolean   # Invalid (contains -)

Naming Conventions

• Use descriptive names (e.g., student_name instead of sn)
• Common styles: camelCase, PascalCase, snake_case

Keywords

Keywords are reserved words in Python. You cannot use them as identifiers.

and, as, assert, break, class, continue, def, del, elif, else, except, 
exec, finally, for, from, global, if, import, in, is, lambda, not, or, 
pass, print, raise, return, try, while, with, yield

Output and Formatting

Basic Output

print('Hello, world!')
print('Welcome to Python programming')

Formatted Output

Use placeholders like %s for strings and %d for integers.

name = 'Alice'
age = 25
print('Name: %s, Age: %d' % (name, age))

Common Format Specifiers

Newline Output

print('Line one\nLine two')

User Input

In Python 3, use input() to read user input. It returns a string.

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

Operators

Arithmetic Operators

a = 10
b = 3
print(a + b)  # Addition
print(a - b)  # Subtraction
print(a * b)  # Multiplication
print(a / b)  # Division
print(a // b) # Floor division
print(a % b)  # Modulus
print(a ** b) # Exponentiation

Assignment Operators

x = 5
x += 3  # Equivalent to x = x + 3

Type Conversion

Convert between types using functions like int(), str(), float().

num_str = '42'
num_int = int(num_str)
print(num_int + 10)  # Output: 52

Conditional Statements

if Statement

user_age = 20
if user_age >= 18:
    print('Access granted')

Comparison and Logical Operators

a = 5
b = 10
if a < b and b > 0:
    print('Conditions met')