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Python is one of the most popular programming languages in the world due to its simple and readable syntax. In this guide, we will look at the basic elements of Python syntax that every novice programmer needs to know.
Comments in Python
Comments in Python start with the character # and are used to add explanations to the code. The Python interpreter ignores comments when executing the program. There are two types of comments:
One-line comments
# This is a one-line
print comment ("Hello world!") # Comment at the end of the line
Multi-line comments
"""
This is a multi-line comment
(documentation line)
Used to describe functions, classes, and modules
"""
'''
An alternative way to create
a multi-line comment
'''
Python indentation
Indentation is a fundamental feature of Python that defines the structure of the code. Unlike other programming languages that use curly braces, Python uses indentation to group code blocks.
Margins rules:
- Standard indentation: 4 spaces
- All lines in the same block must have the same indentation
- Don't mix spaces and tabs
if condition:
# A block of code with an indentation of 4 spaces
perform_action()
another_action()
else:
# Another block of code with the same indentation level
perform another action()
Variables and data types
Python is a dynamically typed language, which means that the type of a variable is determined automatically when a value is assigned.
Main data types:
| Data type | Designation | Example |
|---|---|---|
| Integers | int |
x = 42 |
| Real numbers | float |
y = 3.14 |
| Lines | str |
name = "Python" |
| Boolean values | bool |
is_valid = True |
| Lists | list |
numbers = [1, 2, 3] |
| Tuples | tuple |
coords = (10, 20) |
| Dictionaries | dict |
person = {"name": "Alice"} |
| Sets | set |
unique_nums = {1, 2, 3} |
# Examples of variable declarations
x = 5 # int
y = 3.14 # float
name = "Alice" # str
is_student = True # bool
grades = [85, 90, 78] # list
point = (10, 20) # tuple
student_info = {"name": "Bob", "age": 20} # dict
Operators in Python
Python supports various types of operators for performing mathematical and logical operations.
Arithmetic operators:
x = 10
y = 3
Sum = x + y # 13 - addition
difference = x - y # 7 - subtraction
product = x * y # 30 - multiplication
quotient = x / y # 3.333... - division
integer division = x // y # 3 - integer division
remainder = x % y # 1 - remainder of division
degree = x ** y # 1000 - exponentiation
Comparison operators:
is equal to = x == y # False - equal to not_ equal
to = x != y # True - not equal
to more = x > y # True - more
less = x < y # False - less
is greater than equal = x >= y # True - greater than or equal
to less_ equal = x <= y # False - less than or equal to
Logical operators:
a = True
b = False
and = a and b # False - logical And
or = a or b # True - logical OR
not = not a # False - logical NOT
Conditional expressions
Conditional constructions allow you to execute different blocks of code depending on the conditions.
age = 18
if age >= 18:
print("You are of legal age")
elif age >= 13:
print("You're a teenager")
else:
print("You are a child")
The ternary operator:
# The short form of the conditional expression
status = "adult" if age >= 18 else "minor"
Loops in Python
Loops allow you to perform repetitive operations.
The for loop:
# Iterating over numbers
for i in range(5):
print(f"Iteration of {i}")
# Iterating through the list items
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
print(fruit)
# Iterating over the index
for index, fruit in enumerate(fruits):
print(f"{index}: {fruit}")
The while loop:
count = 0
while count < 5:
print(f"Counter: {count}")
count += 1
Break and continue operators:
for i in range(10):
if i == 3:
continue # Skip the iteration
if i == 7:
break # Exit the
print(i) loop
Functions
The functions allow you to group the code for reuse and better program organization.
def greeting(name, age=None):
"""
Function for greeting the user
Args:
Name (str): User name
age (int, optional): The age of the user
Returns:
str: Welcome message
"""
if age:
return f"Hello, {name}! You are {age} years old."
else:
return f"Hello, {name}!"
# Function call
message = greeting("Anna", 25)
print(message)
Lambda functions:
# Anonymous function
square = lambda x: x ** 2
print(square(5)) # 25
Multi-line instructions
Python provides several ways to write multi-line instructions.
Using parentheses:
# Long
if condition (temperature > 25 and humidity < 60 and
pressure > 1000 and wind speed < 10):
print("Great weather!")
# Long list
of products = [
"bread", "milk", "eggs",
"cheese", "butter", "meat"
]
Using a backslash:
general sum = price_toward1 + price_toward2 + \
price_toward3 + price_toward4
Nested instructions
Python supports nested constructs to create complex logic.
# Nested conditions
if the weather == "sunny":
if the temperature is 20:
if there is a time:
print("Let's go on a picnic!")
else:
print("No time for a picnic")
else:
print("It's too cold")
else:
print("The weather is not suitable")
# Nested loops
for i in range(3):
for j in range(3):
print(f"i={i}, j={j}")
Importing modules
The import system allows you to use additional functions and libraries.
# Import the entire module
import math
result = math.sqrt(16)
# Importing a specific function
from math import sqrt, pi
result = sqrt(16)
# Import with the alias
import numpy as np
array = np.array([1, 2, 3])
# Import of all functions (not recommended)
from math import *
Exception handling
Error handling is an important part of writing reliable code.
try:
number = int(input("Enter a number: "))
result = 10 / number
print(f"Result: {result}")
except ValueError:
print("Error: no number entered")
except ZeroDivisionError:
print("Error: division by zero")
except Exception as e:
print(f"Unexpected error: {e}")
finally:
print("The finally block is always executed")
Working with strings
Strings are one of the most important data types in Python.
# String creation
name = "Python"
description = 'Programming language'
multiline = """
This is a multi
-line string
"""
# Formatting strings
age = 25
# f-strings (recommended method)
message = f"My name is {first name}, I am {age} years old"
# String methods
text = "python programming"
print(text.upper()) # PYTHON PROGRAMMING
print(text.capitalize()) # Python programming
print(text.split()) # ['python', 'programming']
Lists and their methods
Lists are ordered mutable collections of elements.
# Creating a list
of numbers = [1, 2, 3, 4, 5]
mixed = [1, "text", 3.14, True]
#
Number list methods.append(6) # Add
number element.insert(0, 0) # Insert element by
number index.remove(3) # Delete element by value
last = numbers.pop() # Delete and return last element
# List
slices first_three = numbers[:3]
last_three = numbers[-2:]
each_the second = numbers[::2]
Dictionaries
Dictionaries store key-value pairs and provide quick access to data.
# Creating a dictionary
student = {
"name": "Ivan",
"age": 20,
"course": 2,
"estimates": [4, 5, 4, 5]
}
# Working with
print dictionaries(student["name"]) # Ivan
student["specialty"] = "IT" # Add a new
student key.update({"city": "Moscow"}) # Update multiple keys
# Dictionary methods
keys = student.keys()
values = student.values()
items = student.items()