Struggling with lexical scoping and for loops

The second approach may work with few changes:

for b in range(x):    def helper_lambda(c, modifier):        return lambda: current_instance.modify_attr(c, modifier)  # removed event argument    button = tk.Button(button_frame, text="<", command=helper_lambda(b, -1))    button.place(x=110, y=80 + 18 * b)    button = tk.Button(button_frame, text=">", command=helper_lambda(b, 1))    button.place(x=150, y=80 + 18 * b)

However, you can use lambda directly without the helper function:

for b in range(x):    button = tk.Button(button_frame, text="<", command=lambda b=b: current_instance.modify_attr(b, -1))    button.place(x=110, y=80 + 18 * b)    button = tk.Button(button_frame, text=">", command=lambda b=b: current_instance.modify_attr(b, 1))    button.place(x=150, y=80 + 18 * b)

This is a case where functools.partial is a better option than a lambda expression.

from functools import partialfor b in range(x):    button = tk.Button(button_frame, text="<", command=partial(current_instance.modify_attr, b, -1))    button.place(x=110, y=80 + 18 * b)    button = tk.Button(button_frame, text=">", command=partial(current_instance.modify_attr, b, 1))    button.place(x=120, y=80 + 18 * b)

partial receives the value of b as an argument, rather than simply capturing the name b for later use.