Why is this an issue?

Jump statements (return, break, continue, and raise) move control flow out of the current code block. So any statements that come after a jump are dead code.

Noncompliant code example

def fun(a):
  i = 10
  return i + a       # Noncompliant
  i += 1             # this is never executed

Compliant solution

def fun(a):
  i = 10
  return i + a

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