Shared from "Study" on Inkdown
pyenv + venvpyenv is a Python version manager, similar to nvm for Node.js.venv creates an isolated environment for one project, so packages from one project do not affect another.Example:
pyenv install 3.11.6
pyenv local 3.11.6
python -m venv venv
source venv/bin/activate # macOS / Linux
venv\Scripts\activate # Windowspip + requirements.txtpip is Python’s package installer.requirements.txt stores the list of dependencies for a project.Example:
pip install fastapi
pip freeze > requirements.txt
pip install -r requirements.txtPoetry (pyproject.toml)pyproject.toml is the main config file Poetry uses.Example:
poetry init
poetry add fastapi
poetry installipythonipython is a better REPL with autocomplete, command history, and nicer output.Example:
python
>>> 2 + 2
ipython
In [1]: 2 + 2{} like JavaScript or TypeScript.: starts a new block.Example:
if x > 10:
print("big")
else:
print("small")Example:
def add(a: int, b: int) -> int:
return a + bf before the string, then use {} inside it.Example:
name = "Shubho"
age = 21
print(f"My name is {name} and I am {age} years old.")None vs null / undefinedNone to represent “no value”.null or undefined.is None, not == None.Example:
x = None
if x is None:
print("x has no value")False in conditions.None, 0, "", [], {}, set().Example:
items = []
if items:
print("has items")
else:
print("empty"):=Example:
if (length := len("python")) > 5:
print(length)list / dict / set / tuplelist: ordered, mutable collectiondict: key-value mappingset: unordered collection of unique valuestuple: ordered, immutable collectionExample:
my_list = [1, 2, 3]
my_dict = {"name": "Shubho", "age": 21}
my_set = {1, 2, 3}
my_tuple = (1, 2, 3)Example:
nums = [1, 2, 3, 4, 5]
squares = [n * n for n in nums]
print(squares)With condition:
evens = [n for n in nums if n % 2 == 0]
print(evens)Example:
nums = [1, 2, 3]
squares = {n: n * n for n in nums}
print(squares)*args and **kwargs*args collects extra positional arguments into a tuple.**kwargs collects extra keyword arguments into a dictionary.Example:
def show(*args, **kwargs):
print(args)
print(kwargs)
show(1, 2, 3, name="Shubho", role="Engineer")yield)Example:
def count_up_to(n):
for i in range(1, n + 1):
yield i
for num in count_up_to(3):
print(num)Example:
def greet(name, message="Hello"):
print(f"{message}, {name}")
greet("Shubho")
greet("Shubho", message="Welcome")*.Example:
def create_user(name, *, admin=False):
print(name, admin)
create_user("Shubho", admin=True)Example:
def log_call(fn):
def wrapper():
print("Function is running")
return fn()
return wrapper
@log_call
def say_hi():
print("Hi")
say_hi()dataclass__init__ and __repr__.Example:
from dataclasses import dataclass
@dataclass
class User:
name: str
age: int
user = User("Shubho", 21)
print(user)__init__, __str__, __len__, __getitem__.Example:
class Book:
def __init__(self, title):
self.title = title
def __str__(self):
return f"Book: {self.title}"
book = Book("Python Basics")
print(book)with)Example:
with open("notes.txt", "r") as file:
content = file.read()
print(content)try / except / finallytry contains code that may fail.except handles the error.finally always runs, whether there was an error or not.Example:
try:
num = int("abc")
except ValueError as e:
print("Conversion failed:", e)
finally:
print("This always runs")Example:
class AppError(Exception):
pass
raise AppError("Something went wrong in the app")import lets you use code from another file or module.Example:
import math
print(math.sqrt(16))__init__.py__init__.py tells Python that a folder should behave like a package.Example folder structure:
mypackage/
__init__.py
utils.pyImport example:
from mypackage.utils import my_functionExample:
x = 10
x = "hello"Example:
x = "hello"
print(type(x))async / await