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********
Examples
********
Basic round trip of parsing YAML to Python objects, modifying
and generating YAML::
import sys
from ruamel.yaml import YAML
inp = """\
# example
name:
# details
family: Smith # very common
given: Alice # one of the siblings
"""
yaml = YAML()
code = yaml.load(inp)
code['name']['given'] = 'Bob'
yaml.dump(code, sys.stdout)
Resulting in::
# example
name:
# details
family: Smith # very common
given: Bob # one of the siblings
with the old API::
from __future__ import print_function
import sys
import ruamel.yaml
inp = """\
# example
name:
# details
family: Smith # very common
given: Alice # one of the siblings
"""
code = ruamel.yaml.load(inp, ruamel.yaml.RoundTripLoader)
code['name']['given'] = 'Bob'
ruamel.yaml.dump(code, sys.stdout, Dumper=ruamel.yaml.RoundTripDumper)
# the last statement can be done less efficient in time and memory with
# leaving out the end='' would cause a double newline at the end
# print(ruamel.yaml.dump(code, Dumper=ruamel.yaml.RoundTripDumper), end='')
Resulting in ::
# example
name:
# details
family: Smith # very common
given: Bob # one of the siblings
----
YAML handcrafted anchors and references as well as key merging
are preserved. The merged keys can transparently be accessed
using ``[]`` and ``.get()``::
from ruamel.yaml import YAML
inp = """\
- &CENTER {x: 1, y: 2}
- &LEFT {x: 0, y: 2}
- &BIG {r: 10}
- &SMALL {r: 1}
# All the following maps are equal:
# Explicit keys
- x: 1
y: 2
r: 10
label: center/big
# Merge one map
- <<: *CENTER
r: 10
label: center/big
# Merge multiple maps
- <<: [*CENTER, *BIG]
label: center/big
# Override
- <<: [*BIG, *LEFT, *SMALL]
x: 1
label: center/big
"""
yaml = YAML()
data = yaml.load(inp)
assert data[7]['y'] == 2
The ``CommentedMap``, which is the ``dict`` like construct one gets when round-trip loading,
supports insertion of a key into a particular position, while optionally adding a comment::
import sys
from ruamel.yaml import YAML
yaml_str = """\
first_name: Art
occupation: Architect # This is an occupation comment
about: Art Vandelay is a fictional character that George invents...
"""
yaml = YAML()
data = yaml.load(yaml_str)
data.insert(1, 'last name', 'Vandelay', comment="new key")
yaml.dump(data, sys.stdout)
gives::
first_name: Art
last name: Vandelay # new key
occupation: Architect # This is an occupation comment
about: Art Vandelay is a fictional character that George invents...
Please note that the comment is aligned with that of its neighbour (if available).
The above was inspired by a `question <http://stackoverflow.com/a/36970608/1307905>`_
posted by *demux* on StackOverflow.
----
By default ``ruamel.yaml`` indents with two positions in block style, for
both mappings and sequences. For sequences the indent is counted to the
beginning of the scalar, with the dash taking the first position of the
indented "space".
The following program with three dumps::
import sys
from ruamel.yaml import YAML
data = {1: {1: [{1: 1, 2: 2}, {1: 1, 2: 2}], 2: 2}, 2: 42}
yaml = YAML()
yaml.explicit_start = True
yaml.dump(data, sys.stdout)
yaml.indent = 4
yaml.block_seq_indent = 2
yaml.dump(data, sys.stdout)
def sequence_indent_four(s):
# this will fail on direclty nested lists: {1; [[2, 3], 4]}
levels = []
ret_val = ''
for line in s.splitlines(True):
ls = line.lstrip()
indent = len(line) - len(ls)
if ls.startswith('- '):
if not levels or indent > levels[-1]:
levels.append(indent)
elif levels:
if indent < levels[-1]:
levels = levels[:-1]
# same -> do nothing
else:
if levels:
if indent <= levels[-1]:
while levels and indent <= levels[-1]:
levels = levels[:-1]
ret_val += ' ' * len(levels) + line
return ret_val
yaml = YAML()
yaml.explicit_start = True
yaml.dump(data, sys.stdout, transform=sequence_indent_four)
gives as output::
---
1:
1:
- 1: 1
2: 2
- 1: 1
2: 2
2: 2
2: 42
---
1:
1:
- 1: 1
2: 2
- 1: 1
2: 2
2: 2
2: 42
---
1:
1:
- 1: 1
2: 2
- 1: 1
2: 2
2: 2
2: 42
The transform example was inspired by a `question
<https://stackoverflow.com/q/44388701/1307905>`_ posted by *nowox* on
StackOverflow.
|
