如何使多个 if 语句更加“pythonic”和简洁？

Question

I am writing a piece of software that checks the input to a function before passing it to a database. To do this I need to check the type of data before I send it. Right now I am using 5 different if/else statements. How can I condense this and make it easier to read? Thank You!

def addUser(USERNAME, PASSWORD, PHONE, CARRIER, SERVER):
    good = True
    if type(USERNAME) == str and good:
        good = True
    else:
        good = False
    if type(PASSWORD) == str and good:
        good = True
    else:
        good = False
    if type(PHONE) == int and good:
        good = True
    else:
        good = False
    if type(CARRIER) == str and good:
        good = True
    else:
        good = False
    if type(SERVER) == str and good: 
        good = True
    else:
        good = False      

Answer 1

Combine all the conditions into one:

good = type(USERNAME) == str and type(PASSWORD) == str and type(PHONE) == int AND type(CARRIER) == str and type(SERVER) == str

BTW, you generally shouldn't use int for phone numbers. Even though we call them phone numbers we don't perform any numeric operations on them. And putting a phone number in an int variable will lose leading zeroes.

Answer 2

You could loop over all of them. eg:

def check_parameters(params: list):
    for parameter in params:
        if not isinstance(parameter,str):
            return False
    return True


def addUser(USERNAME, PASSWORD, PHONE, CARRIER, SERVER):
    good = check_parameters([USERNAME, PASSWORD, PHONE, CARRIER, SERVER])

Note isinstance(Your_string, str) is preferred to `type() == '

Answer 3

All the conditions must be True. The most pythonic way would be two create two lists — one with the fields and one with their respective types, then compare the two lists and check if all conditions are True. This way you can add any number of fields by appending the fields and types lists. This way you will also avoid one very long statement with multiple conditions and the and operator between them

fields = [USERNAME, PASSWORD, PHONE, CARRIER, SERVER] # append new field if you want
types = [str, str, int, str, str] # append type of new field if you want
good = all(type(field)==types[i] for i, field in enumerate(fields))

Answer 4

To build on JeffUK's answer, you should also raise an error to tell the user which one is wrong if one fails the type test ( "Errors should never pass silently." ):

def check_parameters(params: list):
    for i, parameter in enumerate(params):
        if not isinstance(parameter,str):
            raise ValueError(f'{parameter} in position {i} is {type(parameter)}, not string.')
    return True

You then can wrap your function call in a try block to catch the error.

def addUser(USERNAME, PASSWORD, PHONE, CARRIER, SERVER):
    try:        
        good = check_parameters([USERNAME, PASSWORD, PHONE, CARRIER, SERVER])
    except ValueError as e:
        print(e)

Answer 5

If you are using Python 3.10, a match-case statement might work well for your particular code.

You could also try putting the valid input types into a dictionary, which could condense the code by eliminating the else statements. eg,

data_type_check = {'username': str, 'password': str, 'phone': int,
                   'carrier': str, 'server': str}

for var, key in zip([USERNAME, PASSWORD, PHONE, CARRIER, SERVER], 
                    ['username', 'password', 'phone', 'carrier', 'server']):

    good = type(var) == data_type_check[key]

    if not good:
        break