How to avoid multiple flat if conditions in python?

问题

Consider the snippet:

def check_conditions(range_of_numbers):
#method returns a list containing messages 
    list1 = []
    if condition1:
       list1.append("message1")
    if condition2:
       list1.append("message2")
    if condition3:
       list1.append("message3")
    try:
       for i in range_of_numbers:
           int(i)
    except ValueError:
        list1.append("message4")
    return message

I want to have a list in the with messages only if the conditions were satisfied. I do not use multiple if's since it adds on to the code complexity and every time a new parameter is added I would end up adding a new if condition.

回答1:

just loop on the condition/message couples for instance:

for condition,message in ((condition1,"message1"),(condition2,"message2"),(condition3,"message3")):
    if condition:
       list1.append(message)

if the conditions are exclusive, consider adding a break if one condition matches.

list comprehension version (more "pythonic" but not possible to break on first condition match, though):

list1 = [message for condition,message in ((condition1,"message1"),(condition2,"message2"),(condition3,"message3")) if condition]

回答2:

As a supplement of Jean-FrançoisFabre.

All conditions are satisfied

tmp = [message for condition, message in ((condition1, "message1"),
       (condition2, "message2"),(condition3, "message3")) if condition]

Conditions are exclusive

tmp = next((message for condition, message in ((condition1, "message1"),         
           (condition2, "message2"), (condition3, "message3")) if condition), None)

来源：https://stackoverflow.com/questions/41501833/how-to-avoid-multiple-flat-if-conditions-in-python