Avoiding Syntax Errors with Strings in Python

One kind of error that you might see with some regularity is a syntax error. A syntax error occurs when Python doesn’t recognize a section of your program as valid Python code. For example, if you use an apostrophe within single quotes, you’ll produce an error. This happens because Python interprets everything between the first single quote and the apostrophe as a string. It then tries to interpret the rest of the text as Python code, which causes errors.

Here’s how to use single and double quotes correctly. Save this programas apostrophe.py and then run it:

message = "One of Python's strengths is its diverse community."
print(message)

The apostrophe appears inside a set of double quotes, so the Pythoninterpreter has no trouble reading the string correctly:

One of Python's strengths is its diverse community.

However, if you use single quotes, Python can’t identify where the string should end:

message = 'One of Python's strengths is its diverse community.'
print(message)

You’ll see the following output:

File "apostrophe.py", line 1
message = 'One of Python's strengths is its diverse community.'
SyntaxError: invalid syntax

In the output you can see that the error occurs at u right after the second single quote. This syntax error indicates that the interpreter doesn’t recognize something in the code as valid Python code.

Errors can come from a variety of sources, and I’ll point out some common ones as they arise. You might see syntax errors often as you learn to write proper Python code.

Syntax errors are also the least specific kind of error, so they can be difficult and frustrating to identify and correct. If you get stuck on a particularly stubborn error, see the suggestions in Appendix C.

Your editor’s syntax highlighting feature should help you spot some syntax errors quickly as you write your programs. If you see Python code highlighted as if it’s English or English highlighted as if it’s Python code, you probably have a mismatched quotation mark somewhere in your file.

This article is an excerpt from A Hands-On, Project-Based Introduction to Programming by Eric Matthes

Reproduced with permission from No Starch Press