YAML study notes by Orhan Doğan

# 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
scientific_notation: 1e+12
# The number 1 will be interpreted as a number, not a boolean. if you want
# it to be intepreted as a boolean, use true
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