How do I append one string to another in Python?

How do I efficiently append one string to another? Are there any faster alternatives to:

var1 = "foo"
var2 = "bar"
var3 = var1 + var2

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_{For handling multiple strings in a list, see How to concatenate (join) items in a list to a single string.}

_{See How do I put a variable’s value inside a string (interpolate it into the string)? if some inputs are not strings, but the result should still be a string.}