是否有Python等效于C＃null-coalescing运算符？

#1 楼

other = s or "some default value"

42    or "something"    # returns 42
0     or "something"    # returns "something"
None  or "something"    # returns "something"
False or "something"    # returns "something"
""    or "something"    # returns "something"

#2 楼

other = s if s is not None else "default value"

def notNone(s,d):
    if s is None:
        return d
    else:
        return s

other = notNone(s, "default value")

#3 楼

def coalesce(*arg):
  return reduce(lambda x, y: x if x is not None else y, arg)

# Prints "banana"
print coalesce(None, "banana", "phone", None)

def coalesce(*arg):
  for el in arg:
    if el is not None:
      return el
  return None

#4 楼

{
   name: {
      first: "John",
      last: "Doe"
   }
}

obj.get(property_name, value_if_null)

obj.get("name", {}).get("first", "Name is missing") 

#5 楼

#6 楼

>>> 1 or 5/0
1

object = getCachedVersion() or getFromDB()

#7 楼

def test():
    return

a = 2 if (x:= test()) is None else x

#8 楼

import random

dataset = [random.randint(0,15) if random.random() > .6 else None for i in range(1000)]

def not_none(x, y=None):
    if x is None:
        return y
    return x

def coalesce1(*arg):
  return reduce(lambda x, y: x if x is not None else y, arg)

def coalesce2(*args):
    return next((i for i in args if i is not None), None)

def test_func(dataset, func):
    default = 1
    for i in dataset:
        func(i, default)

>>> %timeit test_func(dataset, not_none)
1000 loops, best of 3: 224 µs per loop

>>> %timeit test_func(dataset, coalesce1)
1000 loops, best of 3: 471 µs per loop

>>> %timeit test_func(dataset, coalesce2)
1000 loops, best of 3: 782 µs per loop

def coalesce(*args, **kwargs):
    default = kwargs.get('default')
    return next((a for a in arg if a is not None), default)

#9 楼

if 'variablename' in globals() and ((variablename or False) == True):
  print('variable exists and it\'s true')
else:
  print('variable doesn\'t exist, or it\'s false')

#10 楼

Python has a get function that its very useful to return a value of an existent key, if the key exist;
if not it will return a default value.

def main():
    names = ['Jack','Maria','Betsy','James','Jack']
    names_repeated = dict()
    default_value = 0

    for find_name in names:
        names_repeated[find_name] = names_repeated.get(find_name, default_value) + 1

#11 楼

def nz(value, none_value, strict=True):
    ''' This function is named after an old VBA function. It returns a default
        value if the passed in value is None. If strict is False it will
        treat an empty string as None as well.

        example:
        x = None
        nz(x,"hello")
        --> "hello"
        nz(x,"")
        --> ""
        y = ""   
        nz(y,"hello")
        --> ""
        nz(y,"hello", False)
        --> "hello" '''

    if value is None and strict:
        return_val = none_value
    elif strict and value is not None:
        return_val = value
    elif not strict and not is_not_null(value):
        return_val = none_value
    else:
        return_val = value
    return return_val 

def is_not_null(value):
    ''' test for None and empty string '''
    return value is not None and len(str(value)) > 0