Rethinking_2 Chp_4: Patsy usage for B-Spline

[jdmoore7]

In section 4.74, the following code block is used:

from patsy import dmatrix
B = dmatrix(
    "bs(year, knots=knots, degree=3, include_intercept=True) -1",
    {"year": d2.year.values, "knots": knot_list[1:-1]},
)

• I'm confused why knot_list[1:-1] is used; not explained in official textbook (to my knowledge) or in code block.
• Not clear on why -1 was used in the formula-like string provided.

From Patsy official documentation:
https://patsy.readthedocs.io/en/latest/API-reference.html#patsy.bs

The - 1 is because one degree of freedom will be taken by the intercept; alternatively, you could leave the intercept term out of your model and use bs(x, num_bins, degree=0, include_intercept=True)

However, I've tried both variants, noting that they produce different results.
Could you describe what effect the declaration of B is supposed to have?