Module: Psych

Defined in:
lib/psych.rb,
psych.c,
parser.c,
to_ruby.c,
emitter.c,
yaml_tree.c,
lib/psych/set.rb,
lib/psych/omap.rb,
lib/psych/nodes.rb,
lib/psych/coder.rb,
lib/psych/parser.rb,
lib/psych/handler.rb,
lib/psych/nodes/node.rb,
lib/psych/deprecated.rb,
lib/psych/nodes/alias.rb,
lib/psych/tree_builder.rb,
lib/psych/nodes/stream.rb,
lib/psych/nodes/scalar.rb,
lib/psych/nodes/mapping.rb,
lib/psych/scalar_scanner.rb,
lib/psych/nodes/sequence.rb,
lib/psych/nodes/document.rb,
lib/psych/visitors/to_ruby.rb,
lib/psych/visitors/emitter.rb,
lib/psych/visitors/visitor.rb,
lib/psych/json/tree_builder.rb,
lib/psych/visitors/json_tree.rb,
lib/psych/visitors/yaml_tree.rb

Overview

Overview

Psych is a YAML parser and emitter. Psych leverages libyaml for it's YAML parsing and emitting capabilities. In addition to wrapping libyaml, Psych also knows how to serialize and de-serialize most Ruby objects to and from the YAML format.

I NEED TO PARSE OR EMIT YAML RIGHT NOW!

# Parse some YAML
Psych.load("--- foo") # => "foo"

# Emit some YAML
Psych.dump("foo")     # => "--- foo\n...\n"
{ :a => 'b'}.to_yaml  # => "---\n:a: b\n"

Got more time on your hands? Keep on reading!

YAML Parsing

Psych provides a range of interfaces for parsing a YAML document ranging from low level to high level, depending on your parsing needs. At the lowest level, is an event based parser. Mid level is access to the raw YAML AST, and at the highest level is the ability to unmarshal YAML to ruby objects.

Low level parsing

The lowest level parser should be used when the YAML input is already known, and the developer does not want to pay the price of building an AST or automatic detection and conversion to ruby objects. See Psych::Parser for more information on using the event based parser.

Mid level parsing

Psych provides access to an AST produced from parsing a YAML document. This tree is built using the Psych::Parser and Psych::TreeBuilder. The AST can be examined and manipulated freely. Please see Psych::parse_stream, Psych::Nodes, and Psych::Nodes::Node for more information on dealing with YAML syntax trees.

High level parsing

The high level YAML parser provided by Psych simply takes YAML as input and returns a Ruby data structure. For information on using the high level parser see Psych.load

YAML Emitting

Psych provides a range of interfaces ranging from low to high level for producing YAML documents. Very similar to the YAML parsing interfaces, Psych provides at the lowest level, an event based system, mid-level is building a YAML AST, and the highest level is converting a Ruby object straight to a YAML document.

Low level emitting

The lowest level emitter is an event based system. Events are sent to a Psych::Emitter object. That object knows how to convert the events to a YAML document. This interface should be used when document format is known in advance or speed is a concern. See Psych::Emitter for more information.

Mid level emitting

At the mid level is building an AST. This AST is exactly the same as the AST used when parsing a YAML document. Users can build an AST by hand and the AST knows how to emit itself as a YAML document. See Psych::Nodes, Psych::Nodes::Node, and Psych::TreeBuilder for more information on building a YAML AST.

High level emitting

The high level emitter has the easiest interface. Psych simply takes a Ruby data structure and converts it to a YAML document. See Psych.dump for more information on dumping a Ruby data structure.

Class Attribute Summary collapse

Class Method Summary collapse

Class Attribute Details

.domain_typesObject

Returns the value of attribute domain_types



236
237
238
# File 'lib/psych.rb', line 236

def domain_types
  @domain_types
end

.dump_tagsObject

Returns the value of attribute dump_tags



235
236
237
# File 'lib/psych.rb', line 235

def dump_tags
  @dump_tags
end

.load_tagsObject

Returns the value of attribute load_tags



234
235
236
# File 'lib/psych.rb', line 234

def load_tags
  @load_tags
end

Class Method Details

.add_builtin_type(type_tag, &block) ⇒ Object



216
217
218
219
220
# File 'lib/psych.rb', line 216

def self.add_builtin_type type_tag, &block
  domain = 'yaml.org,2002'
  key = ['tag', domain, type_tag].join ':'
  @domain_types[key] = [key, block]
end

.add_domain_type(domain, type_tag, &block) ⇒ Object



210
211
212
213
214
# File 'lib/psych.rb', line 210

def self.add_domain_type domain, type_tag, &block
  key = ['tag', domain, type_tag].join ':'
  @domain_types[key] = [key, block]
  @domain_types["tag:#{type_tag}"] = [key, block]
end

.add_private_type(type_tag, &block) ⇒ Object



47
48
49
50
51
52
# File 'lib/psych/deprecated.rb', line 47

def self.add_private_type type_tag, &block
  warn "#{caller[0]}: add_private_type is deprecated, use add_domain_type" if $VERBOSE
  domain = 'x-private'
  key = [domain, type_tag].join ':'
  @domain_types[key] = [key, block]
end

.add_ruby_type(type_tag, &block) ⇒ Object



40
41
42
43
44
45
# File 'lib/psych/deprecated.rb', line 40

def self.add_ruby_type type_tag, &block
  warn "#{caller[0]}: add_ruby_type is deprecated, use add_domain_type" if $VERBOSE
  domain = 'ruby.yaml.org,2002'
  key = ['tag', domain, type_tag].join ':'
  @domain_types[key] = [key, block]
end

.add_tag(tag, klass) ⇒ Object



228
229
230
231
# File 'lib/psych.rb', line 228

def self.add_tag tag, klass
  @load_tags[tag] = klass
  @dump_tags[klass] = tag
end

.detect_implicit(thing) ⇒ Object



33
34
35
36
37
38
# File 'lib/psych/deprecated.rb', line 33

def self.detect_implicit thing
  warn "#{caller[0]}: detect_implicit is deprecated" if $VERBOSE
  return '' unless String === thing
  return 'null' if '' == thing
  ScalarScanner.new.tokenize(thing).class.name.downcase
end

.dump(o, io = nil, options = {}) ⇒ Object

Dump Ruby object o to a YAML string using options.

Example:

Psych.dump(['a', 'b'])  # => "---\n- a\n- b\n"


158
# File 'lib/psych.rb', line 158

def self.dump o, io = nil, options = {}

.dump_stream(*objects) ⇒ Object

Dump a list of objects as separate documents to a document stream.

Example:

Psych.dump_stream("foo\n  ", {}) # => "--- ! \"foo\\n  \"\n--- {}\n"


175
176
177
178
179
180
181
# File 'lib/psych.rb', line 175

def self.dump_stream *objects
  visitor = Psych::Visitors::YAMLTree.new {}
  objects.each do |o|
    visitor << o
  end
  visitor.tree.to_yaml
end

.libyaml_versionObject

Returns the version of libyaml being used



# File 'psych.c'

/* call-seq: Psych.libyaml_version
 *
 * Returns the version of libyaml being used
 */
static VALUE libyaml_version(VALUE module)
{
    int major, minor, patch;
    VALUE list[3];

    yaml_get_version(&major, &minor, &patch);

    list[0] = INT2NUM((long)major);
    list[1] = INT2NUM((long)minor);
    list[2] = INT2NUM((long)patch);

    return rb_ary_new4((long)3, list);
}

.load(yaml) ⇒ Object

Load yaml in to a Ruby data structure. If multiple documents are provided, the object contained in the first document will be returned.

Example:

Psych.load("--- a")           # => 'a'
Psych.load("---\n - a\n - b") # => ['a', 'b']


105
106
107
108
# File 'lib/psych.rb', line 105

def self.load yaml
  result = parse(yaml)
  result ? result.to_ruby : result
end

.load_documents(yaml, &block) ⇒ Object



24
25
26
27
28
29
30
31
# File 'lib/psych/deprecated.rb', line 24

def self.load_documents yaml, &block
  if $VERBOSE
    warn "#{caller[0]}: load_documents is deprecated, use load_stream"
  end
  list = load_stream yaml
  return list unless block_given?
  list.each(&block)
end

.load_file(filename) ⇒ Object

Load the document contained in filename. Returns the yaml contained in filename as a ruby object



204
205
206
# File 'lib/psych.rb', line 204

def self.load_file filename
  self.load File.open(filename)
end

.load_stream(yaml) ⇒ Object

Load multiple documents given in yaml. Returns the parsed documents as a list. For example:

Psych.load_stream("--- foo\n...\n--- bar\n...") # => ['foo', 'bar']


197
198
199
# File 'lib/psych.rb', line 197

def self.load_stream yaml
  parse_stream(yaml).children.map { |child| child.to_ruby }
end

.object_maker(klass, hash) ⇒ Object



70
71
72
73
74
75
# File 'lib/psych/deprecated.rb', line 70

def self.object_maker klass, hash
  warn "#{caller[0]}: object_maker is deprecated" if $VERBOSE
  klass.allocate.tap do |obj|
    hash.each { |k,v| obj.instance_variable_set(:@#{k}", v) }
  end
end

.parse(yaml) ⇒ Object

Parse a YAML string in yaml. Returns the first object of a YAML AST.

Example:

Psych.parse("---\n - a\n - b") # => #<Psych::Nodes::Sequence:0x00>

See Psych::Nodes for more information about YAML AST.



118
119
120
121
# File 'lib/psych.rb', line 118

def self.parse yaml
  children = parse_stream(yaml).children
  children.empty? ? false : children.first.children.first
end

.parse_file(filename) ⇒ Object

Parse a file at filename. Returns the YAML AST.



125
126
127
128
129
# File 'lib/psych.rb', line 125

def self.parse_file filename
  File.open filename do |f|
    parse f
  end
end

.parse_stream(yaml) ⇒ Object

Parse a YAML string in yaml. Returns the full AST for the YAML document. This method can handle multiple YAML documents contained in yaml.

Example:

Psych.parse_stream("---\n - a\n - b") # => #<Psych::Nodes::Stream:0x00>

See Psych::Nodes for more information about YAML AST.



146
147
148
149
150
# File 'lib/psych.rb', line 146

def self.parse_stream yaml
  parser = self.parser
  parser.parse yaml
  parser.handler.root
end

.parserObject

Returns a default parser



133
134
135
# File 'lib/psych.rb', line 133

def self.parser
  Psych::Parser.new(TreeBuilder.new)
end

.quick_emit(thing, opts = {}, &block) ⇒ Object

:nodoc:



11
12
13
14
15
16
17
18
19
20
21
22
# File 'lib/psych/deprecated.rb', line 11

def self.quick_emit thing, opts = {}, &block 
  warn "#{caller[0]}: YAML.quick_emit is deprecated" if $VERBOSE && !caller[0].start_with?(File.dirname(__FILE__))
  target = eval 'self', block.binding
  target.extend DeprecatedMethods
  metaclass = class << target; self; end
  metaclass.send(:define_method, :encode_with) do |coder|
    target.taguri        = coder.tag
    target.to_yaml_style = coder.style
    block.call coder
  end
  target.psych_to_yaml unless opts[:nodump]
end

.read_type_class(type, reference) ⇒ Object



60
61
62
63
64
65
66
67
68
# File 'lib/psych/deprecated.rb', line 60

def self.read_type_class type, reference
  warn "#{caller[0]}: read_type_class is deprecated" if $VERBOSE
  _, _, type, name = type.split ':', 4

  reference = name.split('::').inject(reference) do |k,n|
    k.const_get(n.to_sym)
  end if name
  [type, reference]
end

.remove_type(type_tag) ⇒ Object



222
223
224
# File 'lib/psych.rb', line 222

def self.remove_type type_tag
  @domain_types.delete type_tag
end

.tagurize(thing) ⇒ Object



54
55
56
57
58
# File 'lib/psych/deprecated.rb', line 54

def self.tagurize thing
  warn "#{caller[0]}: add_private_type is deprecated, use add_domain_type" if $VERBOSE
  return thing unless String === thing
  "tag:yaml.org,2002:#{thing}"
end

.to_json(o) ⇒ Object

Dump Ruby object o to a JSON string.



185
186
187
188
189
# File 'lib/psych.rb', line 185

def self.to_json o
  visitor = Psych::Visitors::JSONTree.new
  visitor << o
  visitor.tree.to_yaml
end