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I need to write the below data to yaml file using Python:

{A:a, B:{C:c, D:d, E:e}}

i.e., dictionary in a dictionary. How can I achieve this?

dreftymac
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user1643521
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2 Answers2

244
import yaml

data = dict(
    A = 'a',
    B = dict(
        C = 'c',
        D = 'd',
        E = 'e',
    )
)

with open('data.yml', 'w') as outfile:
    yaml.dump(data, outfile, default_flow_style=False)

The default_flow_style=False parameter is necessary to produce the format you want (flow style), otherwise for nested collections it produces block style:

A: a
B: {C: c, D: d, E: e}
Cornflex
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Matthew Trevor
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    default_flow_style=True does the opposite as stated in the answer below! – encc Jul 28 '14 at 13:04
  • Is there a benefit of using `with` here as opposed to the one-liner? – src Jun 19 '19 at 14:21
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    @src `with` ensures the file is closed properly when it is no longer needed – kbolino Jun 27 '19 at 19:42
  • See [Munch](https://pypi.org/project/munch/), https://stackoverflow.com/questions/52570869/load-yaml-as-nested-objects-instead-of-dictionary-in-python `import yaml; from munch import munchify; f = munchify(yaml.safe_load(…));print(f.B.C)` – Hans Ginzel Jun 21 '20 at 21:23
93

Link to the PyYAML documentation showing the difference for the default_flow_style parameter. To write it to a file in block mode (often more readable):

d = {'A':'a', 'B':{'C':'c', 'D':'d', 'E':'e'}}
with open('result.yml', 'w') as yaml_file:
    yaml.dump(d, yaml_file, default_flow_style=False)

produces:

A: a
B:
  C: c
  D: d
  E: e
Anthon
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lou
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  • See [Munch](https://pypi.org/project/munch/), https://stackoverflow.com/questions/52570869/load-yaml-as-nested-objects-instead-of-dictionary-in-python `import yaml; from munch import munchify; f = munchify(yaml.safe_load(…));print(f.B.C)` – Hans Ginzel Jun 21 '20 at 21:24