evaluating a string with variable assignments

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Suppose I have a long string of Sage code that performs some variable assignment. I'd like to evaluate it so that those variables become defined in the Sage session. For the sake of simplicity, let it be:

cmd = 'a=1;b=2;'
sage_eval('None',cmds=cmd)
print(a)

This particular code evaluates cmd successfully but the variable values are lost upon completion of sage_eval, which is not what I want. Is it possible to evaluate cmd with keeping all variables assigned?

PS. I know a workaround with a,b = sage_eval('a,b',cmds=cmd) but I'd like to avoid explicit communication of variable values.