我想用Python编写一个函数,根据输入索引的值返回不同的固定值。

在其他语言中,我会使用switch或case语句,但Python似乎没有switch语句。在此场景中,推荐的Python解决方案是什么?


当前回答

运行函数的解决方案:

result = {
    'case1':     foo1, 
    'case2':     foo2,
    'case3':     foo3,
}.get(option)(parameters_optional)

其中foo1()、foo2()和foo3()是函数

示例1(带参数):

option = number['type']
result = {
    'number':     value_of_int,  # result = value_of_int(number['value'])
    'text':       value_of_text, # result = value_of_text(number['value'])
    'binary':     value_of_bin,  # result = value_of_bin(number['value'])
}.get(option)(value['value'])

示例2(无参数):

option = number['type']
result = {
    'number':     func_for_number, # result = func_for_number()
    'text':       func_for_text,   # result = func_for_text()
    'binary':     func_for_bin,    # result = func_for_bin()
}.get(option)()

示例4(仅限值):

option = number['type']
result = {
    'number':    lambda: 10,       # result = 10
    'text':      lambda: 'ten',    # result = 'ten'
    'binary':    lambda: 0b101111, # result = 47
}.get(option)()

其他回答

我在谷歌搜索上找不到简单的答案。但我还是想通了。这真的很简单。决定把它贴出来,也许可以防止别人的头上少刮几下。关键是简单的“in”和元组。下面是带有直通的switch语句行为,包括RANDOM直通。

l = ['Dog', 'Cat', 'Bird', 'Bigfoot',
     'Dragonfly', 'Snake', 'Bat', 'Loch Ness Monster']

for x in l:
    if x in ('Dog', 'Cat'):
        x += " has four legs"
    elif x in ('Bat', 'Bird', 'Dragonfly'):
        x += " has wings."
    elif x in ('Snake',):
        x += " has a forked tongue."
    else:
        x += " is a big mystery by default."
    print(x)

print()

for x in range(10):
    if x in (0, 1):
        x = "Values 0 and 1 caught here."
    elif x in (2,):
        x = "Value 2 caught here."
    elif x in (3, 7, 8):
        x = "Values 3, 7, 8 caught here."
    elif x in (4, 6):
        x = "Values 4 and 6 caught here"
    else:
        x = "Values 5 and 9 caught in default."
    print(x)

提供:

Dog has four legs
Cat has four legs
Bird has wings.
Bigfoot is a big mystery by default.
Dragonfly has wings.
Snake has a forked tongue.
Bat has wings.
Loch Ness Monster is a big mystery by default.

Values 0 and 1 caught here.
Values 0 and 1 caught here.
Value 2 caught here.
Values 3, 7, 8 caught here.
Values 4 and 6 caught here
Values 5 and 9 caught in default.
Values 4 and 6 caught here
Values 3, 7, 8 caught here.
Values 3, 7, 8 caught here.
Values 5 and 9 caught in default.
class switch(object):
    value = None
    def __new__(class_, value):
        class_.value = value
        return True

def case(*args):
    return any((arg == switch.value for arg in args))

用法:

while switch(n):
    if case(0):
        print "You typed zero."
        break
    if case(1, 4, 9):
        print "n is a perfect square."
        break
    if case(2):
        print "n is an even number."
    if case(2, 3, 5, 7):
        print "n is a prime number."
        break
    if case(6, 8):
        print "n is an even number."
        break
    print "Only single-digit numbers are allowed."
    break

测验:

n = 2
#Result:
#n is an even number.
#n is a prime number.
n = 11
#Result:
#Only single-digit numbers are allowed.

还可以使用列表存储案例,并通过select调用相应的函数-

cases = ['zero()', 'one()', 'two()', 'three()']

def zero():
  print "method for 0 called..."
def one():
  print "method for 1 called..."
def two():
  print "method for 2 called..."
def three():
  print "method for 3 called..."

i = int(raw_input("Enter choice between 0-3 "))

if(i<=len(cases)):
  exec(cases[i])
else:
  print "wrong choice"

也在螺丝台上进行了解释。

如果你有一个复杂的大小写块,你可以考虑使用函数字典查找表。。。

如果您以前没有这样做过,那么最好进入调试器并查看字典如何查找每个函数。

注意:不要在大小写/字典查找中使用“()”,否则将在创建字典/大小写块时调用每个函数。记住这一点,因为您只想使用哈希样式查找调用每个函数一次。

def first_case():
    print "first"

def second_case():
    print "second"

def third_case():
    print "third"

mycase = {
'first': first_case, #do not use ()
'second': second_case, #do not use ()
'third': third_case #do not use ()
}
myfunc = mycase['first']
myfunc()

易于记忆:

while True:
    try:
        x = int(input("Enter a numerical input: "))
    except:
        print("Invalid input - please enter a Integer!");
    if x==1:
        print("good");
    elif x==2:
        print("bad");
    elif x==3:
        break
    else:
        print ("terrible");