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Keyword can't be an expression error with subs()

asked 2018-09-25 12:49:12 -0600

trbillin gravatar image

I want to be able to iterate through a list of variables for function and make assignments to each of them. Here's an example that shows the issue I'm having:

R.<x,y> = PolynomialRing(QQ,2)
f = x^2+y^2
variables = [x,y]
f.subs(variables[0]=1)

This gives "SyntaxError: keyword can't be an expression." How can I get around this? The goal is to use a loop to make substitutions for some variables, look at what happens, then in the next iteration different substitutions will be made.

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answered 2018-09-25 15:18:46 -0600

tmonteil gravatar image

Instead of passing variables[0] as the name of an argument, you can pass a dictionary as an argument of subs method:

sage: R.<x,y> = PolynomialRing(QQ,2)
....: f = x^2+y^2
....: variables = [x,y]
....: f.subs({variables[0]:1})
y^2 + 1
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Thank you, this fixed the issue!

trbillin gravatar imagetrbillin ( 2018-09-25 19:33:42 -0600 )edit

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Asked: 2018-09-25 12:49:12 -0600

Seen: 127 times

Last updated: Sep 25