CodeQL documentation

Formatting string mixes implicitly and explicitly numbered fields

ID: py/str-format/mixed-fields
Kind: problem
Security severity: 
Severity: error
Precision: high
   - reliability
   - correctness
Query suites:
   - python-security-and-quality.qls

Click to see the query in the CodeQL repository

A formatting expression, that is an expression of the form the_format.format(args) or format(the_format, args), can use explicitly numbered fields, like {1}, or implicitly numbered fields, such as {}, but it cannot use both. Doing so will raise a ValueError.


Use either explicitly numbered fields or implicitly numbered fields, but be consistent.


In the following example the formatting uses both implicit, {}, and explicit, {1}, numbering for fields, which is illegal.

def illegal_format():
    "{} {1}".format("spam", "eggs")


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