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percent-format-expected-mapping (F502)

Added in v0.0.142 · Related issues · View source

Derived from the Pyflakes linter.

What it does

Checks for named placeholders in printf-style format strings without mapping-type values.

Why is this bad?

When using named placeholders in printf-style format strings, the values must be a map type (such as a dictionary). Otherwise, the expression will raise a TypeError.

Example

"%(greeting)s, %(name)s" % ("Hello", "World")

Use instead:

"%(greeting)s, %(name)s" % {"greeting": "Hello", "name": "World"}

Or:

"%s, %s" % ("Hello", "World")

References