Python function - if input variable doesn't exist then use default value

Question

def funcname(var1, var2 = "1234"):

    output = int(var2)

    return output

Is there a way to catch error in case where var2 does not exist i.e. function defines a default value (above) and is called:

result = funcname(var1, var2 = cs) 

but cs does not exist so in case where cs variable does not exist I would like var2 to inherit the default value rather that error as cs not defined.

Answer 1

In your situation you can use try/except

try: 
    result = function(var1, cs) 
except NameError: 
    result = function(var1)

But I would rather create variable cs at start with default value

cs = "1234"

and there is no problem with not existing variable.

Eventually I would use None

cs = None

and function would use None to recognize if it should use default value

#def funcname(var1, var2=None):
def funcname(var1, var2="1234"):
    if var2 is None:
        var2 = "1234"
    return int(var2)

---

In some tutorials/books I saw also var2=object when None is correct value which shouldn't be replaced or it should be replaced with different value then default value.

I neved had to use object for this so I'm not sure if I use it correctly in this example.

cs = None

def func(var1, var2=object):
    if var2 == object:
        var2 = "1234"
    elif var2 is None:
        var2 = "0"
    return int(var2)

print(func(1))       # 1234
print(func(1, 2))    # 2
print(func(1, None)) # 0
print(func(1, cs))   # 0

---

But I thing that the best would be create variable cs at start with some value.