Python Syntax

Syntax is the set of rules for how Python code must be written. Python’s rules are few, but one of them, indentation, is stricter than in most languages. Learn these rules once and most beginner errors disappear.

Statements and lines

A Python program is a list of statements, normally one per line. Python runs them from top to bottom. No semicolon is needed at the end of a line.

city = "Pune"temperature = 31print(city, temperature)

Pune 31

Indentation defines blocks

Many languages use curly braces { } to group lines. Python uses indentation: the spaces at the start of a line. A line ending in a colon : starts a block, and every line in that block must be indented by the same amount.

score = 82 if score >= 50:    print("Passed")          # inside the if block    print("Well done")       # also insideprint("Report finished")     # outside: runs every time

Passed
Well done
Report finished

Wrong indentation is a syntax error, and Python refuses to run the file:

if True:print("not indented")

  File "main.py", line 2
    print("not indented")
    ^^^^^
IndentationError: expected an indented block after 'if' statement on line 1

Indenting a line that should not be indented is also an error:

print("one")    print("two")

  File "main.py", line 2
    print("two")
IndentationError: unexpected indent

Blocks inside blocks

Each new block adds one more level of indentation. Python knows a block has ended when the indentation goes back.

for n in [1, 2, 3, 4]:    if n % 2 == 0:        print(n, "is even")    else:        print(n, "is odd")print("done")

1 is odd
2 is even
3 is odd
4 is even
done

Long lines

Python ends a statement at the end of the line, except inside brackets (), [] or {}. So the easiest way to split a long line is to wrap it in parentheses.

total = (    120    + 80    + 45)names = ["login", "search",         "checkout"]print(total, names)

245 ['login', 'search', 'checkout']

A backslash \ at the end of a line also continues it, but brackets are clearer and are what the PEP 8 style guide recommends.

Several statements on one line

A semicolon lets you put two statements on one line. It works, but it hurts readability, so use it rarely.

a = 1; b = 2; print(a + b)

3

Case sensitivity

Python is case-sensitive: name, Name and NAME are three different variables, and Print is not the same as print.

name = "Asha"Name = "Ravi"print(name, Name)Print("hello")

Asha Ravi
Traceback (most recent call last):
  File "main.py", line 4, in <module>
    Print("hello")
    ^^^^^
NameError: name 'Print' is not defined. Did you mean: 'print'?

Keywords

Keywords are reserved words with a special meaning, such as if, for and def. You cannot use them as variable names. The keyword module lists them:

import keywordprint(len(keyword.kwlist))print(keyword.kwlist)

35
['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

Check your understanding

x = 5if x > 3:    print("big")print("end")if x > 10:    print("huge")

big
end

print("Even numbers:")for n in range(1, 7):    if n % 2 == 0:        print(n)print("Done")

Even numbers:
2
4
6
Done

Program Practice

Python syntax FAQ