Скачать или смотреть Fixing PyCharm's Expected type 'SupportsIndex | slice', got 'str' instead Error with CSV DictReader

Learn how to resolve type hint errors in PyCharm when accessing CSV rows with DictReader in Python by using precise type annotations.
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This video is based on the question https://stackoverflow.com/q/79498617/ asked by the user 'Charles Knell' ( https://stackoverflow.com/u/2039866/ ) and on the answer https://stackoverflow.com/a/79512567/ provided by the user 'Charles Knell' ( https://stackoverflow.com/u/2039866/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem

When reading CSV files in Python using csv.DictReader, each row is a dictionary with string keys and values. However, PyCharm may incorrectly warn with the error:

[[See Video to Reveal this Text or Code Snippet]]

This happens when you access a dictionary item like row['SYMBOL']. The code runs fine but the IDE's static type checker is confused about the type of row.

Why the Warning Occurs

PyCharm relies on type hints to verify your code. Without explicit hints, it may infer row as a generic Mapping or an unknown type that doesn't support string indexing explicitly.

Clear and Simple Solution: Add a Type Hint

By providing a type hint that explicitly declares row as a dictionary with string keys and string values, you guide PyCharm’s type checker:

[[See Video to Reveal this Text or Code Snippet]]

What this does:

row: dict[str, str] tells PyCharm “here, treat row exactly as a dictionary with strings as keys and values.”

This silence the type warning without changing runtime behavior.

Alternative Approaches

At function level: Declare the type hint in the for loop variable (Python 3.10+ supports this directly):

[[See Video to Reveal this Text or Code Snippet]]

Using typing module:

[[See Video to Reveal this Text or Code Snippet]]

However, adding a simple inline hint as shown above is often the easiest fix.

Summary

PyCharm static analyzer sometimes misinterprets CSV DictReader’s rows.

Explicitly type hint each row as dict[str, str] to fix the warning.

This is a quick, non-intrusive way to improve code clarity and avoid false positives without changing functionality.

Now your CSV reading code will be both Pythonic and free of confusing IDE warnings!