How can I define a function with default parameter values and optional parameters in Python?

Question

I want to define a function to which the input parameters can be omitted or have a default value.

I have this function:

def nearxy(x,y,x0,y0,z):
   distance=[]
   for i in range(0,len(x)):   
   distance.append(abs(math.sqrt((x[i]-x0)**2+(y[i]-y0)**2)))
   ...
   return min(distance)

I want make x0 and y0 have a default value, and make z optional if I don't have a z value.

How can I do that? Thank you.

Answer 1

You can't make function arguments optional in Python, but you can give them default values. So:

def nearxy(x, y, x0=0, y0=0, z=None):
    ...

That makes x0 and y0 have default values of 0 , and z have a default value of None .

Assuming None makes no sense as an actual value for z , you can then add logic in the function to do something with z only if it's not None .

Answer 2

def nearxy(x, y, x0 = 0, y0 = 0, z = None):
   ...

Check if z is None to see if it has been omitted.

Answer 3

give default values to x0,y0 like this and if z is optional also :

def nearxy(x,y,x0=0,y0=0,z=None):
   distance=[]
   for i in range(0,len(x)):   
   distance.append(abs(math.sqrt((x[i]-x0)**2+(y[i]-y0)**2)))
   if z is not None:
        blah blah
   return min(distance)

call :

nearxy(1,2)

if you want only toassign z :

 nearxy(1,2,z=3)

....

hope this helps

Answer 4

To specify a default value, define the parameter with a '=' and then the value.

An argument where a default value is specified is an optional argument.

For example, if you wanted x0 , y0 , and z to have default values of 1,2,3:

def nearxy(x,y,x0=1,y0=2,z=3):
   distance=[]
   for i in range(0,len(x)):   
       distance.append(abs(math.sqrt((x[i]-x0)**2+(y[i]-y0)**2)))
   ...
   return min(distance)

See http://docs.python.org/2/tutorial/controlflow.html#default-argument-values for more.