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A dead store happens when a local variable is assigned a value that is not read by any subsequent instruction. Calculating or retrieving a value
only to then overwrite it or throw it away, could indicate a serious error in the code. Even if it's not an error, it is at best a waste of resources.
Therefore all calculated values should be used.
Noncompliant Code Example
def func(a, b, compute):
    i = a + b  # Noncompliant; calculation result not used before value is overwritten
    i = compute()  # Noncompliant; the value is not used before leaving the function

Compliant Solution
def func(a, b, compute):
    i = a + b
    i += compute()
    return i

Exceptions
This rule ignores initializations to -1, 0, 1, None, True, False and "".
No issue will be raised on unpacked variables.
See

   MITRE, CWE-563 - Assignment to Variable without Use ('Unused Variable') 
   CERT, MSC13-C. - Detect and remove unused values 
   CERT, MSC56-J. - Detect and remove superfluous code and values