If I had a class with a function like the following and I wanted to have two variables that had default values:
class item:
def __init__(self, var1=1, var2=2)
self.var1 = var1
self.var2 = var2
How could I create an instance of this class and change var2's value but not var1's?
a = item(#Leave var1 alone, but set var2 to 'hello')
You would just instantiate it like:
# leave var1 as default
a = item(var2='hello')
# leave var2 as default
a = item(var1='hey')
# overwrite both var1 and var2
a = item(var1='hey', var2='hello')
# use both defaults
a = item()
The thing to note in your example in the comment is you must now provide a var1 since it has no default. So item(var1=1, var3=2) and item(1, var3=2) would both work, while item(var3=2) would not. Also keyword arguments must come last when there are arguments without default values, so item(var3=2, 1) would also not work but item(var3=2, var1=1) would.
Use named parameters when instantiating:
a = item(var2=42)
This would leave var1 to its default value of 1, but set var2 to 42.
The following script shows this in action:
class item:
def __init__(self, var1=1, var2=2):
self.var1 = var1
self.var2 = var2
a = item()
print a.var1
print a.var2
b = item(var2=42)
print b.var1
print b.var2
The output of that is, as desired:
1
2
1
42
