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---
language: yaml
filename: learnyaml.yaml
contributors:
- ["Adam Brenecki", "https://github.com/adambrenecki"]
- ["Suhas SG", "https://github.com/jargnar"]
---
YAML is a data serialisation language designed to be directly writable and
readable by humans.
It's a strict superset of JSON, with the addition of syntactically
significant newlines and indentation, like Python. Unlike Python, however,
YAML doesn't allow literal tab characters at all.
```yaml
# Comments in YAML look like this.
################
# SCALAR TYPES #
################
# Our root object (which continues for the entire document) will be a map,
# which is equivalent to a dictionary, hash or object in other languages.
key: value
another_key: Another value goes here.
a_number_value: 100
# If you want to use number 1 as a value, you have to enclose it in quotes,
# otherwise, YAML parser will assume that it is a boolean value of true.
scientific_notation: 1e+12
boolean: true
null_value: null
key with spaces: value
# Notice that strings don't need to be quoted. However, they can be.
however: "A string, enclosed in quotes."
"Keys can be quoted too.": "Useful if you want to put a ':' in your key."
# Multiple-line strings can be written either as a 'literal block' (using |),
# or a 'folded block' (using '>').
literal_block: |
This entire block of text will be the value of the 'literal_block' key,
with line breaks being preserved.
The literal continues until de-dented, and the leading indentation is
stripped.
Any lines that are 'more-indented' keep the rest of their indentation -
these lines will be indented by 4 spaces.
folded_style: >
This entire block of text will be the value of 'folded_style', but this
time, all newlines will be replaced with a single space.
Blank lines, like above, are converted to a newline character.
'More-indented' lines keep their newlines, too -
this text will appear over two lines.
####################
# COLLECTION TYPES #
####################
# Nesting is achieved by indentation.
a_nested_map:
key: value
another_key: Another Value
another_nested_map:
hello: hello
# Maps don't have to have string keys.
0.25: a float key
# Keys can also be complex, like multi-line objects
# We use ? followed by a space to indicate the start of a complex key.
? |
This is a key
that has multiple lines
: and this is its value
# YAML also allows mapping between sequences with the complex key syntax
# Some language parsers might complain
# An example
? - Manchester United
- Real Madrid
: [ 2001-01-01, 2002-02-02 ]
# Sequences (equivalent to lists or arrays) look like this:
a_sequence:
- Item 1
- Item 2
- 0.5 # sequences can contain disparate types.
- Item 4
- key: value
another_key: another_value
-
- This is a sequence
- inside another sequence
# Since YAML is a superset of JSON, you can also write JSON-style maps and
# sequences:
json_map: {"key": "value"}
json_seq: [3, 2, 1, "takeoff"]
#######################
# EXTRA YAML FEATURES #
#######################
# YAML also has a handy feature called 'anchors', which let you easily duplicate
# content across your document. Both of these keys will have the same value:
anchored_content: &anchor_name This string will appear as the value of two keys.
other_anchor: *anchor_name
# Anchors can be used to duplicate/inherit properties
base: &base
name: Everyone has same name
foo: &foo
<<: *base
age: 10
bar: &bar
<<: *base
age: 20
# foo and bar would also have name: Everyone has same name
# YAML also has tags, which you can use to explicitly declare types.
explicit_string: !!str 0.5
# Some parsers implement language specific tags, like this one for Python's
# complex number type.
python_complex_number: !!python/complex 1+2j
# We can also use yaml complex keys with language specific tags
? !!python/tuple [5, 7]
: Fifty Seven
# Would be {(5, 7): 'Fifty Seven'} in python
####################
# EXTRA YAML TYPES #
####################
# Strings and numbers aren't the only scalars that YAML can understand.
# ISO-formatted date and datetime literals are also parsed.
datetime: 2001-12-15T02:59:43.1Z
datetime_with_spaces: 2001-12-14 21:59:43.10 -5
date: 2002-12-14
# The !!binary tag indicates that a string is actually a base64-encoded
# representation of a binary blob.
gif_file: !!binary |
R0lGODlhDAAMAIQAAP//9/X17unp5WZmZgAAAOfn515eXvPz7Y6OjuDg4J+fn5
OTk6enp56enmlpaWNjY6Ojo4SEhP/++f/++f/++f/++f/++f/++f/++f/++f/+
+f/++f/++f/++f/++f/++SH+Dk1hZGUgd2l0aCBHSU1QACwAAAAADAAMAAAFLC
AgjoEwnuNAFOhpEMTRiggcz4BNJHrv/zCFcLiwMWYNG84BwwEeECcgggoBADs=
# YAML also has a set type, which looks like this:
set:
? item1
? item2
? item3
# Like Python, sets are just maps with null values; the above is equivalent to:
set2:
item1: null
item2: null
item3: null
```
|
