What is Python’s SyntaxError: invalid syntax?

One of the very first errors you’ll likely encounter when learning Python is SyntaxError: invalid syntax. This error occurs when your code violates Python’s grammatical rules. In simple terms, the Python interpreter cannot understand what you’ve written.

While this error can stem from a wide range of issues, it’s most often caused by a simple mistake. This guide will walk you through the most common causes and their solutions.

1. Missing Colon (:)

In Python, statements that start a code block—such as if, for, def, and class—must end with a colon (:). Forgetting it will result in a SyntaxError.

Incorrect Code:

if True
    print("A colon is missing.")

Corrected Code:

if True:
    print("A colon is missing.")

Simply adding a colon at the end of the block-starting statement resolves the issue.

2. Mismatched Parentheses, Brackets, or Braces

Parentheses (), brackets [], and braces {} must always exist in pairs. An opening bracket must have a corresponding closing bracket.

Incorrect Code:

my_list = [1, 2, 3
print(my_list)

Corrected Code:

my_list = [1, 2, 3]
print(my_list)

Carefully review your code to find the missing bracket and complete the pair. In complex code, your editor’s bracket highlighting feature can be a great help.

3. Using the Wrong Assignment Operator

You must use the = operator to assign a value to a variable. Using the comparison operator == for assignment will cause a SyntaxError.

Incorrect Code:

x == 5 # Using a comparison operator for assignment

Corrected Code:

x = 5

This mistake is especially common inside if statements, so be extra careful there.

4. Mismatched Quotes

A string must be enclosed by either single (') or double (") quotes. If you start with one type and end with another, or forget to close the string entirely, you’ll get an error.

Incorrect Code:

message = "Hello' # Mismatched start and end quotes

Corrected Code:

message = "Hello"

5. Misspelled Keywords

A typo in one of Python’s reserved keywords (e.g., if, for, while, def) will lead to a syntax error.

Incorrect Code:

whlie True: # Misspelled 'while' as 'whlie'
    print("Infinite loop")

Corrected Code:

while True:
    print("Infinite loop")

Conclusion

SyntaxError: invalid syntax is usually caused by a minor grammatical mistake. While the error message can be frustratingly vague, you can solve most cases by calmly checking the following:

  • Ensure there is a colon (:) at the end of every block-starting statement.
  • Check that all parentheses (), brackets [], and braces {} are correctly paired.
  • Verify you are using = for assignment.
  • Make sure all strings are properly closed with matching quotes.
  • Check for typos in keywords.

By developing these habits, you’ll be able to fix SyntaxError much more quickly and efficiently when it appears.

Leave a comment

You may also enjoy