I am doing a pygame physics tutorial. However, when I try putting Round Bracket inside Round Bracket in Def Function, it says "Invalid Syntax". I could not find a answer anywhere.
def addVectors((angle1, length1), (angle2, length2)):
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Why is it so critical to have that particular syntax? – Mad Physicist Jan 16 '22 at 17:17
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Because of `(self.angle, self.speed) = addVectors((self.angle, self.speed), gravity)` – ChinDaMay Jan 16 '22 at 17:21
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*"I could not find a answer anywhere"* - answer to what? I can't see a question... You show a wrong syntax you wrote. Why do you expect it to work? What do you ***expect*** it to do? – Tomerikoo Jan 16 '22 at 17:44
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@Tomerikoo Turns out it only works in python 2. – ChinDaMay Jan 16 '22 at 17:50
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1Does this answer your question? [Python can't define tuples in a function (duplicate)](https://stackoverflow.com/q/20035591/6045800) – Tomerikoo Jan 16 '22 at 17:52
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Yes, but someone already answered it below. – ChinDaMay Jan 16 '22 at 20:37
3 Answers
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That only works in Python 2 sadly:
>$ python2
Python 2.7.18 (default, Mar 8 2021, 13:02:45)
[GCC 9.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> def addVectors((angle1, length1), (angle2, length2)):
... pass
...
>>>
>$ python3
Python 3.8.8 (default, Apr 13 2021, 19:58:26)
[GCC 7.3.0] :: Anaconda, Inc. on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def addVectors((angle1, length1), (angle2, length2)):
File "<stdin>", line 1
def addVectors((angle1, length1), (angle2, length2)):
^
SyntaxError: invalid syntax
I suggest using a namedtuple:
from collections import namedtuple
Vector = namedtuple('Vector', ['angle', 'length'])
v1 = Vector(angle=1, length=1)
v2 = Vector(angle=2, length=1)
def addVectors(v1, v2):
return Vector(v1.angle + v2.angle, v1.length + v2.length)
Caridorc
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the implementation of the vector sum is wrong, it is just to give you an idea of how to use the `namedtuple` – Caridorc Jan 16 '22 at 17:11
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1You really don't need to make up a separate type for this. Just unpack the parameters on the first line. – Mad Physicist Jan 16 '22 at 17:41
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@MadPhysicist yes of course, it depends on personal preference in the end. the unpacking at the start is also a reasonable option – Caridorc Jan 16 '22 at 18:09
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You are trying to pass a tuple by parameter but this way is the wrong syntax way. Try something like that:
def addVectors(*angles):
for i in angles:
print(i)
# addVectors((angle1, length1), (angle2, length2))
# (1, 2)
# (3, 4)
The * will unpack like a list and you can pass any size of parameters
Franz Kurt
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1How would I Integrate that with: `def addVectors(angle1, length1, angle2, length2): x = math.sin(angle1)*length1 +math.sin(angle2)*length2 y = math.cos(angle1)*length1 +math.cos(angle2)*length2 angle = 0.5*math.pi -math.atan2(y,x) length = math.hypot(x,y) return(angle, length)` – ChinDaMay Jan 16 '22 at 17:05
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Given your specific example, you can hopefully see why the syntax you are looking for is error prone. Imagine what happens when you accidentally mess up a single parenthesis 6 months from now. You have a couple of options to implement the same functionality trivially in Python 3 with fewer parentheses.
If you want the input to be four objects:
def addVectors(angle1, length1, angle2, length2):
...
and call as
self.angle, self.speed = addVectors(self.angle, self.speed, *gravity)
If you want two inputs, you can specify an explicit unpacking:
def addVectors(vector1, vector2):
angle1, length1 = vector1
angle2, length2 = vector2
...
and call it as
self.angle, self.speed = addVectors((self.angle, self.speed), gravity)
As you can see, there's no reason to give up on Python 3 just because of this syntax.
Mad Physicist
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