prize17-4, Exercise 2: Stride in B-flat

bass = {"Bb": ("Bb1", "F2"), "Eb": ("Eb2", "Bb2")}
chord = {"Bb": "Bb-D-F", "Eb": "Eb-G-Bb"}
for name in ("Bb", "Eb"):
    low, alt = bass[name]
    print(name, "|", low, chord[name], alt, chord[name])

Output (run and checked):

Bb | Bb1 Bb-D-F F2 Bb-D-F
Eb | Eb2 Eb-G-Bb Bb2 Eb-G-Bb

Why it works: each chord needs a low root and a fifth above it. The fifth of B-flat is F, and the fifth of E-flat is B-flat. The number after each note name is its octave; 1 and 2 are low notes.

Care: octave numbers are a choice. A pianist picks the ones that keep the bass below the chord.