New submission from Martin Meo <martin....@gmail.com>:
"""
Unexpected behavior report
Dictionary get(key, default-expression) not short circuit behavior
MacOS 10.14.6
sys.version_info(major=3, minor=6, micro=5, releaselevel='final', serial=0)
BACKGROUND
A python dictionary is a data structure that associates a set of keys with a
set of values.
Accessing a non-existent key produces a KeyError.
Dictionaries have a get() method.
get(key[, default-expression])
Return the value for key if key is in the dictionary, else default-expression.
If default-expression is not given, it defaults to None, so that this method
never raises a KeyError.
EXPECTED BEHAVIOR
get() would only evaluate default-expression if it has to, when key is not
found. It would have short-circuit behavior like boolean operators.
ACTUAL BEHAVIOR
The default-expression DOES get evaluated even when the key IS found in the
dictionary. And if default-expression is a function call, the function DOES get
called.
"""
denominations = {0:'zero', 1:'one', 2:'two', 3:'three', 4:'four'}
def foo(n):
print('FOO CALLED. n =', n)
return str(n*10)
words = []
words.append(denominations[1])
words.append(denominations[4])
words.append(denominations.get(1))
words.append(denominations.get(4))
words.append(denominations.get(1, 'ERROR-A'))
words.append(denominations.get(4, 'ERROR-B'))
words.append(denominations.get(22, 'ERROR-1'))
words.append(denominations.get(88, 'ERROR-2'))
words.append(denominations.get(1, foo(1)))
words.append(denominations.get(4, foo(4)))
print(words)
def isItZero(n):
print('ISITZERO CALLED. n=', n)
return False
a = (True or isItZero(9)) # (True or x) is always True so x is not evaluated
----------
messages: 358602
nosy: martinmeo
priority: normal
severity: normal
status: open
title: Dictionary get(key, default-expression) not short circuit behavior
type: behavior
versions: Python 3.7
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue39083>
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