Python in 10 Minutes

Name on the left, value on the right, done. No type declarations, no semicolons. Skip type hints for now too — you'll meet them later and they'll make sense then.

name = "Ada"          # string
age = 36              # integer
height = 1.7          # float
is_ready = True       # capital T — true will crash
nothing = None        # Python's "null", capital N

print(name, age)      # Ada 36

Python has three ways to format strings. Ignore two of them. % formatting and .format() exist in old tutorials and old codebases — you only ever need to write f-strings: an f before the quote, variables in braces.

name = "Ada"
msgs = 5
print(f"Hi {name}, you have {msgs} messages")

# the four methods that cover 90% of real string work:
s = "  Swift Grasp  "
s.strip()             # "Swift Grasp"   — trim whitespace
s.lower()             # for case-insensitive compares
s.split()             # ['Swift', 'Grasp']
", ".join(["a", "b"])  # "a, b" — yes, join lives on the separator

There are no curly braces. A colon opens a block, and the indentation is the syntax. This is the number one source of day-one crashes, so let's deal with it head-on.

score = 87

if score >= 90:
    print("A")
elif score >= 80:
    print("B")               # this one runs
else:
    print("keep going")

# and / or / not are words, not && || !
if 80 <= score < 90:          # chained compare — very Python
    print("solid B")

label = "pass" if score >= 60 else "fail"

The container you'll use daily: ordered, mixable, grows as needed. Two ideas carry most of the weight — negative indexes count from the end, and slices cut ranges out.

langs = ["python", "js", "rust"]

langs.append("go")       # add to end
langs[0]                 # "python"
langs[-1]                # "go" — last item, no len() dance
langs[1:3]               # ['js', 'rust'] — end index not included
len(langs)               # 4
"rust" in langs          # True

nums = [3, 1, 2]
sorted(nums)             # new sorted copy: [1, 2, 3]
nums.sort()              # sorts in place, returns None (!)

Key–value pairs, like a JSON object. I'd estimate half of working Python is passing dicts around, so learn one habit early: square brackets when the key must exist, .get() when it might not.

user = {"name": "Ada", "age": 36}

user["name"]                   # "Ada"
user["role"] = "admin"         # add or overwrite

user.get("email")              # None — no crash
user.get("email", "n/a")       # "n/a" — with a default

for key, value in user.items():
    print(f"{key} = {value}")

Python's for walks the items directly — if you're writing for i in range(len(things)), stop, there's always a cleaner way. Need the index too? That's what enumerate is for.

for lang in ["python", "js", "rust"]:
    print(lang)

for i, lang in enumerate(["a", "b"]):
    print(i, lang)           # 0 a, then 1 b

for i in range(3):            # just numbers: 0, 1, 2
    print(i)

count = 3
while count > 0:
    count -= 1                # there is no count-- in Python

Define with def, hand back results with return. Defaults make arguments optional, and calling with names — greet(excited=True) — keeps call sites readable six months later.

def greet(name, excited=False):
    msg = f"Hello, {name}"
    return msg + "!" if excited else msg

greet("Ada")                   # Hello, Ada
greet("Ada", excited=True)     # Hello, Ada!

# returning two things (it's a tuple, unpacked on arrival)
def min_max(nums):
    return min(nums), max(nums)

lo, hi = min_max([3, 1, 9])    # lo=1, hi=9

Build a new list in one line: transform on the left, loop in the middle, filter on the right. One honest rule — if it needs more than one if or a nested loop, write a normal loop instead. Clever one-liners are how you lose an afternoon.

nums = [1, 2, 3, 4, 5]

squares = [n * n for n in nums]           # [1, 4, 9, 16, 25]
evens = [n for n in nums if n % 2 == 0]   # [2, 4]

# dict version
lengths = {w: len(w) for w in ["hi", "hello"]}
# {'hi': 2, 'hello': 5}

Always open files with with — it closes them for you even if the code crashes halfway. And always pass encoding="utf-8". Tutorials skip it because it works on their Mac; on Windows the default encoding is different and real files will bite you.

with open("notes.txt", "w", encoding="utf-8") as f:
    f.write("line one\n")

with open("notes.txt", encoding="utf-8") as f:
    for line in f:               # line by line, any file size
        print(line.strip())

# JSON in and out — you'll do this weekly
import json
with open("data.json", "w", encoding="utf-8") as f:
    json.dump({"name": "Ada"}, f)

Two skills here. First: when a traceback appears, read the last line first — that's the actual error; the lines above it are just the trail. Second: catch specific error types. A bare except: swallows every bug in the block and you will spend hours finding what it ate.

try:
    age = int("not a number")
except ValueError:
    print("that wasn't a number")

try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"oops: {e}")

# raise your own when input is nonsense
def set_age(age):
    if age < 0:
        raise ValueError("age can't be negative")

Honest take: you can write useful Python for weeks without defining a class, so don't stall here. Learn to read them — __init__ runs at creation, self is the object talking about itself — and move on. When your dicts start feeling unruly, come back.

class Dog:
    def __init__(self, name):
        self.name = name
        self.tricks = []

    def learn(self, trick):
        self.tricks.append(trick)
        return f"{self.name} learned {trick}"

rex = Dog("Rex")
rex.learn("sit")
rex.tricks                     # ['sit']

The lines everyone googles a hundred times. Bookmark this section; that's what it's for.

# swap two variables
a, b = b, a

# reverse a list or string
nums[::-1]

# dedupe, keeping order (list(set(x)) scrambles order — avoid)
list(dict.fromkeys(items))

# most common element
from collections import Counter
Counter(words).most_common(1)

# merge two dicts (right side wins on conflicts)
merged = {**defaults, **overrides}

# read input from the user
name = input("Name: ")

# install a package / run a script (in the terminal)
# pip install requests
# python script.py

That's the working core of the language. The way it sticks is not more reading — pick something tiny and annoying in your life (renaming a folder of files, a to-do list in the terminal) and build it. You now know enough.