ruamel - block_seq_indent and indent - yaml

Question

I have been struggling with getting my YAML file with correct indentation after using yaml.round_trip_dump. I am trying to figure what is the difference between block_seq_indent and indent. Couldn't really find anything useful in the documentation as well.

Answer 1

indent is the normal indent that ruamel.yaml inherited from PyYAML. It affects both mapping keys and sequences elements. For sequences that means it doesn't affect the hash ('-') before a sequence element.
So if you run:
import sys
import ruamel.yaml
d = dict(a=1, b=[1, 2, {3: [3.1, 3.2, 3.3]}], c=dict(d=1, e=2))
ruamel.yaml.safe_dump(d, sys.stdout, default_flow_style=False, explicit_start=True)
ruamel.yaml.safe_dump(d, sys.stdout, default_flow_style=False, indent=4, explicit_start=True)
The output will be:
---
a: 1
b:
- 1
- 2
- 3:
- 3.1
- 3.2
- 3.3
c:
d: 1
e: 2
---
a: 1
b:
- 1
- 2
- 3:
- 3.1
- 3.2
- 3.3
c:
d: 1
e: 2
If you also provide block_seq_indent you can do:
ruamel.yaml.safe_dump(d, sys.stdout, default_flow_style=False, indent=4,
block_seq_indent=3, explicit_start=True)
to get:
a: 1
b:
- 1
- 2
- 3:
- 3.1
- 3.2
- 3.3
c:
d: 1
e: 2
To have even more control you should use the new ruamel.yaml API where you can do:
yaml = ruamel.yaml.YAML()
yaml.indent(mapping=3, sequence=5, offset=2)
yaml.explicit_start = True
yaml.dump(d, sys.stdout)
to get:
a: 1
b:
- 1
- 2
- 3:
- 3.1
- 3.2
- 3.3
c:
d: 1
e: 2
i.e. you can use offset to position the dash within the spaces that are the indent for the sequence elements.
This is documented here