Question

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How to break a line of chained methods in Python?

Following question is about python codestyle and may be design of reusable lib. So I have builder that chains graph creation into single big line as follow:

graph.builder() \
        .push(root) \
        .push(n1) \
        .arc(arcType) \ #root-arc-n1 error is there
        .push(n2) \
...

At line #4 I get the error about wrong symbol (#). So general question how to produce well commented code against long builder path. Also as a good answer I’ll appreciate suggestion on changes in builder to allow comments for clarifying code.

Answer 1

Wrapping the entire thing in parentheses forces python to treat it as a single expression:

(graph.builder()
    .push(root)
    .push(n1)
    .arc(arcType) #root-arc-n1 error is there
    .push(n2)
)

I might be tempted to rework your builder method to allow:

graph.builder(lambda g: g
    .push(root)
    .push(n1)
    .arc(arcType) #root-arc-n1 error is there
    .push(n2)
)

Just to make the location of parentheses more sensible