import sqlite3 conn = sqlite3.connect("shop.db")cur = conn.cursor()cur.execute("DROP TABLE IF EXISTS products")cur.execute("""    CREATE TABLE products (        id INTEGER PRIMARY KEY AUTOINCREMENT,        name TEXT NOT NULL,        category TEXT,        price REAL,        stock INTEGER DEFAULT 0    )""")conn.commit()print(cur.execute("SELECT name FROM sqlite_master WHERE type='table'").fetchall())conn.close()

[('products',), ('sqlite_sequence',)]

import sqlite3 conn = sqlite3.connect("shop.db")cur = conn.cursor()cur.execute("INSERT INTO products (name, category, price, stock) VALUES (?, ?, ?, ?)",            ("Keyboard", "electronics", 1499.0, 25)) items = [    ("Mouse", "electronics", 349.0, 60),    ("Notebook", "stationery", 45.0, 300),    ("Pen", "stationery", 10.0, 0),    ("Monitor", "electronics", 12999.0, 8),]cur.executemany("INSERT INTO products (name, category, price, stock) VALUES (?, ?, ?, ?)", items)conn.commit()print("last id:", cur.lastrowid, "rows:", cur.execute("SELECT COUNT(*) FROM products").fetchone()[0])conn.close()

last id: 1 rows: 5

import sqlite3 conn = sqlite3.connect("shop.db")cur = conn.cursor() for row in cur.execute("SELECT id, name, price FROM products ORDER BY price DESC LIMIT 3"):    print(row) cur.execute("SELECT name FROM products WHERE category = ? AND stock > ?", ("electronics", 10))print(cur.fetchall()) print(cur.execute("SELECT AVG(price) FROM products WHERE category = 'stationery'").fetchone())conn.close()

(5, 'Monitor', 12999.0)
(1, 'Keyboard', 1499.0)
(2, 'Mouse', 349.0)
[('Keyboard',), ('Mouse',)]
(27.5,)

import sqlite3 conn = sqlite3.connect("shop.db")conn.row_factory = sqlite3.Rowrow = conn.execute("SELECT * FROM products WHERE name = ?", ("Mouse",)).fetchone()print(row["name"], row["price"], row["stock"])print(dict(row))conn.close()

Mouse 349.0 60
{'id': 2, 'name': 'Mouse', 'category': 'electronics', 'price': 349.0, 'stock': 60}

import sqlite3 conn = sqlite3.connect("shop.db")cur = conn.cursor()cur.execute("UPDATE products SET price = ROUND(price * 0.9, 2) WHERE category = ?", ("electronics",))print("discounted:", cur.rowcount)cur.execute("DELETE FROM products WHERE stock = 0")print("deleted:", cur.rowcount)conn.commit()print(conn.execute("SELECT name, price FROM products ORDER BY id").fetchall())conn.close()

discounted: 3
deleted: 1
[('Keyboard', 1349.1), ('Mouse', 314.1), ('Notebook', 45.0), ('Monitor', 11699.1)]

import sqlite3 conn = sqlite3.connect("shop.db")try:    with conn:        conn.execute("UPDATE products SET stock = stock - 5 WHERE name = 'Monitor'")        conn.execute("INSERT INTO products (name) VALUES (NULL)")   # violates NOT NULLexcept sqlite3.IntegrityError as e:    print("rolled back:", e) print(conn.execute("SELECT stock FROM products WHERE name = 'Monitor'").fetchone())conn.close()

rolled back: NOT NULL constraint failed: products.name
(8,)

import sqlite3 conn = sqlite3.connect(":memory:")conn.executescript("""    CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT);    CREATE TABLE orders (id INTEGER PRIMARY KEY, user_id INTEGER, amount REAL);    INSERT INTO users VALUES (1, 'Asha'), (2, 'Ravi'), (3, 'Meena');    INSERT INTO orders VALUES (1, 1, 500), (2, 1, 250), (3, 3, 900);""")query = """    SELECT u.name, COUNT(o.id), COALESCE(SUM(o.amount), 0)    FROM users u LEFT JOIN orders o ON o.user_id = u.id    GROUP BY u.id ORDER BY u.name"""for row in conn.execute(query):    print(row)conn.close()

('Asha', 2, 750.0)
('Meena', 1, 900.0)
('Ravi', 0, 0)

import sqlite3import pandas as pd conn = sqlite3.connect("shop.db")df = pd.read_sql_query("SELECT name, category, price FROM products", conn)print(df)print(df.groupby("category")["price"].mean().round(1).to_dict())conn.close()

       name     category    price
0  Keyboard  electronics   1349.1
1     Mouse  electronics    314.1
2  Notebook   stationery     45.0
3   Monitor  electronics  11699.1
{'electronics': 4454.1, 'stationery': 45.0}

results = {"login": "pass", "search": "pass", "checkout": "fail"} passed = [name for name, status in results.items() if status == "pass"]print("Tests run:", len(results))print("Passed:", ", ".join(passed))

Tests run: 3
Passed: login, search

value = 42print(type(value)) value = "forty-two"print(type(value))

<class 'int'>
<class 'str'>

import this

The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

import sys, platform print(platform.python_implementation())print(sys.version_info.major, sys.version_info.minor)

CPython
3 15

def total(numbers):    result = 0    for n in numbers:        result += n    return result print(total([6, 9, 4, 5, 3]))

27

import numpy as npimport pandas as pddf = pd.DataFrame({"name": ["Alex", "John", "Peter", "Klaus"], "age": [30, np.nan, 29, np.nan]})print(df[df["age"].isna()])

    name  age
1   John  NaN
3  Klaus  NaN

import pandas as pda, b = pd.Series([1, 6, 9, 5]), pd.Series([5, 2, 4, 5])print((a > b).tolist())

[False, True, True, False]

for ch in ["A", "g", "5"]:    if ch.isupper():        print(ch, "is an uppercase letter")    else:        print(ch, "is not an uppercase letter")

A is an uppercase letter
g is not an uppercase letter
5 is not an uppercase letter