2.1.3. patsy.builtins.Q

patsy.builtins.Q(name)

A way to ‘quote’ variable names, especially ones that do not otherwise meet Python’s variable name rules.

If x is a variable, Q("x") returns the value of x. (Note that Q takes the string "x", not the value of x itself.) This works even if instead of x, we have a variable name that would not otherwise be legal in Python.

For example, if you have a column of data named weight.in.kg, then you can’t write:

y ~ weight.in.kg

because Python will try to find a variable named weight, that has an attribute named in, that has an attribute named kg. (And worse yet, in is a reserved word, which makes this example doubly broken.) Instead, write:

y ~ Q("weight.in.kg")

and all will be well. Note, though, that this requires embedding a Python string inside your formula, which may require some care with your quote marks. Some standard options include:

my_fit_function("y ~ Q('weight.in.kg')", ...)
my_fit_function('y ~ Q("weight.in.kg")', ...)
my_fit_function("y ~ Q(\"weight.in.kg\")", ...)

Note also that Q is an ordinary Python function, which means that you can use it in more complex expressions. For example, this is a legal formula:

y ~ np.sqrt(Q("weight.in.kg"))