Python: passing flags to functions

Question

For a long time i have been trying to figure out what is the best way to pass flags to python functions. The most straightforward way is something like:

def func(data, flag1, flag2, flag3):
    ...

func(my_data, True, False, True)

This is really nice and concise, but incredibly hard to read, since the word "True" or "False" tells you nothing about what flag is being set, and you have to carefully count the arguments starting from the left. You can make them keyword arguments:

def func(data, flag1=False, flag2=False, flag3=False):
    ...

func(my_data, flag1=True, flag3=True)

but this is kind of redundant, since the "True" doesn't carry any meaning at all. I could pass it as a list:

func(mydata, ['flag1', 'flag3'])

or

func(mydata, [func.flag1, func.flag3])

But the first feels rather dirty, using strings as flags, and the second is still somewhat repetitive. Ideally i want to say something like:

func(my_data, flag1, flag3)

to pass flags to a function with minimal verbosity and redundancy. Is there any way to do something like this in python?

EDIT: I ended up going with:

func(mydata, flagA=1, flagB=1)

mostly for the reasons mentioned: compile-time checking (versus passing in strings), no namespace pollution (as opposed to using global "ENUM"s) and minimal boilerplate (=1 or =0 is only 2 characters, vs 5 or 6 for =True or =False). It also makes setting default values for the flags very easy:

def func(data, flagA=1, flagB=0, flagC=1):
    ...

which is far more clear and far more easy than jumping through hoops to extract and assign defaults to **kwarg-style flags. The flags are basically statically checked and very clear/clean to write. Now if only I could shave off the last two characters...

Answer 1

you can define flag1 ...flagN as global variables, and define your function with func( *args)

FLAG1 = 1
FLAG2 = 2

def func(*args):
   pass

func(FLAG1, FLAG2)

By defining flags separately, instead of using string, you can avoid typos in flags' names and some headache when debugging

Answer 2

Some Python standard libraries use this:

re.match(pattern, str, re.MULTILINE | re.IGNORECASE)

You can tweak this approach by using *args:

my.func(a, b, c, my.MULTLINE, my.IGNORECASE)

I would really recommend going with flag1=True:

• it is readable
• flag name is checked at compile time (unless **kwargs is used)
• you can use flag=1 and flag=0 instead of True and False to reduce the noise
• you can temporarily change LONG_FLAG_NAME_YOU_DONT_REMEMBER=True to False without retyping the long name when you will need to change back