TypeError: got multiple values for argument
This happens when a keyword argument is specified that overwrites a positional argument. For example, let's imagine a function that draws a colored box. The function selects the color to be used and delegates the drawing of the box to another function, relaying all extra arguments.
def color_box(color, *args, **kwargs):
painter.select_color(color)
painter.draw_box(*args, **kwargs)
Then the call
color_box("blellow", color="green", height=20, width=30)
will fail because two values are assigned to color
: "blellow"
as positional and "green"
as keyword. (painter.draw_box
is supposed to accept the height
and width
arguments).
This is easy to see in the example, but of course if one mixes up the arguments at call, it may not be easy to debug:
# misplaced height and width
color_box(20, 30, color="green")
Here, color
is assigned 20
, then args=[30]
and color
is again assigned "green"
.
I had the same problem that is really easy to make, but took me a while to see through.
I had copied the declaration to where I was using it and had left the 'self' argument there, but it took me ages to realise that.
I had
self.myFunction(self, a, b, c='123')
but it should have been
self.myFunction(a, b, c='123')
This also happens if you forget self
declaration inside class methods.
Example:
class Example():
def is_overlapping(x1, x2, y1, y2):
# Thanks to https://stackoverflow.com/a/12888920/940592
return max(x1, y1) <= min(x2, y2)
Fails calling it like self.is_overlapping(x1=2, x2=4, y1=3, y2=5)
with:
{TypeError} is_overlapping() got multiple values for argument 'x1'
WORKS:
class Example():
def is_overlapping(self, x1, x2, y1, y2):
# Thanks to https://stackoverflow.com/a/12888920/940592
return max(x1, y1) <= min(x2, y2)
This exception also will be raised whenever a function has been called with the combination of keyword arguments
and args
, kwargs
Example:
def function(a, b, c, *args, **kwargs):
print(f"a: {a}, b: {b}, c: {c}, args: {args}, kwargs: {kwargs}")
function(a=1, b=2, c=3, *(4,))
And it'll raise:
TypeError Traceback (most recent call last)
<ipython-input-4-1dcb84605fe5> in <module>
----> 1 function(a=1, b=2, c=3, *(4,))
TypeError: function() got multiple values for argument 'a'
And Also it'll become more complicated, whenever you misuse it in the inheritance. so be careful we this stuff!
1- Calling a function with keyword arguments
and args
:
class A:
def __init__(self, a, b, *args, **kwargs):
self.a = a
self.b = b
class B(A):
def __init__(self, *args, **kwargs):
a = 1
b = 2
super(B, self).__init__(a=a, b=b, *args, **kwargs)
B(3, c=2)
Exception:
TypeError Traceback (most recent call last)
<ipython-input-5-17e0c66a5a95> in <module>
11 super(B, self).__init__(a=a, b=b, *args, **kwargs)
12
---> 13 B(3, c=2)
<ipython-input-5-17e0c66a5a95> in __init__(self, *args, **kwargs)
9 a = 1
10 b = 2
---> 11 super(B, self).__init__(a=a, b=b, *args, **kwargs)
12
13 B(3, c=2)
TypeError: __init__() got multiple values for argument 'a'
2- Calling a function with keyword arguments
and kwargs
which it contains keyword arguments too:
class A:
def __init__(self, a, b, *args, **kwargs):
self.a = a
self.b = b
class B(A):
def __init__(self, *args, **kwargs):
a = 1
b = 2
super(B, self).__init__(a=a, b=b, *args, **kwargs)
B(**{'a': 2})
Exception:
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-7-c465f5581810> in <module>
11 super(B, self).__init__(a=a, b=b, *args, **kwargs)
12
---> 13 B(**{'a': 2})
<ipython-input-7-c465f5581810> in __init__(self, *args, **kwargs)
9 a = 1
10 b = 2
---> 11 super(B, self).__init__(a=a, b=b, *args, **kwargs)
12
13 B(**{'a': 2})
TypeError: __init__() got multiple values for keyword argument 'a'
Simply put you can't do the following:
class C(object):
def x(self, y, **kwargs):
# Which y to use, kwargs or declaration?
pass
c = C()
y = "Arbitrary value"
kwargs["y"] = "Arbitrary value"
c.x(y, **kwargs) # FAILS
Because you pass the variable 'y' into the function twice: once as kwargs and once as function declaration.