Practice Python 3 right here — no installs, no signups.
Python's readable syntax makes it the most popular first language in the world, and this online Python 3 compiler removes the only real barrier left: installation. Write a script, press Run, read the output — including tracebacks, which are printed in full so you can practise reading them.
The runner supports the standard library, standard input, loops, comprehensions, functions, classes, dictionaries, file-free string handling, and exception handling. It is ideal for school and college assignments, interview prep, and working through the Python chapters on this site.
Copy any snippet into the editor above and press Run. Each one is short on purpose — retype it from memory afterwards.
marks = {"Aarav": 78, "Priya": 91, "Rohan": 55}
toppers = [name for name, m in marks.items() if m > 70]
print("Toppers:", toppers)
print("Average:", sum(marks.values()) / len(marks))A comprehension replaces a four-line for loop with one readable expression.
name = input("Your name: ")
n = int(input("A number: "))
for i in range(1, n + 1):
print(f"{name} x {i} = {i}")Type the input values in the stdin box under the editor before pressing Run — one value per line.
IndentationError: expected an indented block
Why: The line after a colon is not indented.
Fix: Indent the body by four spaces. Never mix tabs and spaces in one file.
TypeError: can only concatenate str (not "int") to str
Why: You joined a number to a string with +.
Fix: Wrap it: "Age: " + str(age), or use an f-string: f"Age: {age}".
NameError: name 'x' is not defined
Why: The variable is used before assignment or is misspelled.
Fix: Assign it earlier; remember Python is case sensitive.
| Concept | Syntax |
|---|---|
| Print with formatting | print(f"{name} is {age}") |
| List comprehension | [x * 2 for x in nums if x > 0] |
| Function | def add(a, b): return a + b |
| Class | class Dog:\n def __init__(self, n): self.n = n |
| Dict loop | for k, v in d.items(): |
| Exception | try: ... except ValueError as e: ... |
Python 3, so f-strings, type hints and the modern standard library are all available.
Yes. Put each value on its own line in the standard input box below the editor before running.
Running snippets builds speed; the 17-chapter course builds understanding. Work through the Python 3 chapters, take the quiz, then claim your certificate.
Other compilers: JavaScript compiler, TypeScript compiler, Java compiler, C compiler, C++ compiler, Go compiler, Rust compiler, HTML compiler, CSS compiler, SQLite compiler
After these steps you can write Python that reads input, makes decisions, loops over data, groups values in lists and dictionaries, and organises logic into functions and classes.
Python has no braces: a block is defined by consistent indentation, conventionally four spaces. Mixing tabs and spaces is the single most common beginner error.
age = 20
if age >= 18:
print("adult")
else:
print("minor")An f-string embeds expressions directly in a string literal and is the clearest way to build output.
name = "Aarav"
marks = 87.456
print(f"{name} scored {marks:.1f}")for-in walks a sequence directly. Use enumerate when you genuinely need the position, and range only for counting.
subjects = ["math", "science", "code"]
for i, s in enumerate(subjects, start=1):
print(i, s)A list keeps order and duplicates, a dict maps keys to values, a set stores unique items and tests membership fast. Picking the right one is most of good Python.
marks = {"math": 91, "code": 78}
marks["science"] = 64
print(sorted(marks.items(), key=lambda kv: -kv[1]))Functions take arguments and return values; a class bundles data with the functions that act on it. Default arguments make functions easier to call.
class Student:
def __init__(self, name, marks):
self.name = name
self.marks = marks
def passed(self, cutoff=50):
return self.marks >= cutoff
print(Student("Diya", 47).passed())Try each one in the editor above before opening the solution — the struggle is where the learning happens.
Hint: range(1, 11) stops before 11.
for i in range(1, 11):
print(f"7 x {i} = {7 * i}")Hint: dict.get(key, 0) avoids a KeyError on the first occurrence.
word = "programming"
counts = {}
for ch in word:
counts[ch] = counts.get(ch, 0) + 1
print(counts)Hint: yield inside a while loop; the generator stays lazy.
def fib(limit):
a, b = 0, 1
while a < limit:
yield a
a, b = b, a + b
print(sum(fib(100)))Python's syntax is close to plain English, so you spend your attention on the problem rather than on punctuation.
It is the default language of data analysis, machine learning and automation, which means most tutorials and libraries in those fields assume Python.
Ready for structured practice? The 17-chapter Python 3 course takes these ideas one at a time, with a quiz and a certificate at the end.