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/stream.rb,
lib/psych/handler.rb,
lib/psych/streaming.rb,
lib/psych/deprecated.rb,
lib/psych/nodes/node.rb,
lib/psych/nodes/alias.rb,
lib/psych/json/stream.rb,
lib/psych/nodes/scalar.rb,
lib/psych/syntax_error.rb,
lib/psych/tree_builder.rb,
lib/psych/nodes/stream.rb,
lib/psych/nodes/mapping.rb,
lib/psych/nodes/sequence.rb,
lib/psych/nodes/document.rb,
lib/psych/scalar_scanner.rb,
lib/psych/json/ruby_events.rb,
lib/psych/visitors/visitor.rb,
lib/psych/visitors/to_ruby.rb,
lib/psych/visitors/emitter.rb,
lib/psych/json/yaml_events.rb,
lib/psych/json/tree_builder.rb,
lib/psych/visitors/json_tree.rb,
lib/psych/visitors/yaml_tree.rb,
lib/psych/visitors/depth_first.rb,
lib/psych/handlers/document_stream.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.

Defined Under Namespace

Modules: DeprecatedMethods, Handlers, JSON, Nodes, Streaming, Visitors Classes: BadAlias, Coder, Emitter, Exception, Handler, Omap, Parser, ScalarScanner, Set, Stream, SyntaxError, TreeBuilder

Constant Summary collapse

VERSION =

The version is Psych you're using

'1.3.2'
LIBYAML_VERSION =

The version of libyaml Psych is using

Psych.libyaml_version.join '.'
DEPRECATED =

:nodoc:

__FILE__

Class Attribute Summary collapse

Class Method Summary collapse

Class Attribute Details

.domain_types ⇒ Object

Returns the value of attribute domain_types



328
329
330
 
# File 'lib/psych.rb', line 328

def domain_types
  @domain_types
end

.dump_tags ⇒ Object

Returns the value of attribute dump_tags



327
328
329
 
# File 'lib/psych.rb', line 327

def dump_tags
  @dump_tags
end

.load_tags ⇒ Object

Returns the value of attribute load_tags



326
327
328
 
# File 'lib/psych.rb', line 326

def load_tags
  @load_tags
end

Class Method Details

.add_builtin_type(type_tag, &block) ⇒ Object 



308
309
310
311
312
 
# File 'lib/psych.rb', line 308

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 



302
303
304
305
306
 
# File 'lib/psych.rb', line 302

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 



320
321
322
323
 
# File 'lib/psych.rb', line 320

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

call-seq:

Psych.dump(o)               -> string of yaml
Psych.dump(o, options)      -> string of yaml
Psych.dump(o, io)           -> io object passed in
Psych.dump(o, io, options)  -> io object passed in

Dump Ruby object o to a YAML string. Optional options may be passed in to control the output format. If an IO object is passed in, the YAML will be dumped to that IO object.

Example:

# Dump an array, get back a YAML string
Psych.dump(['a', 'b'])  # => "---\n- a\n- b\n"

# Dump an array to an IO object
Psych.dump(['a', 'b'], StringIO.new)  # => #<StringIO:0x000001009d0890>

# Dump an array with indentation set
Psych.dump(['a', ['b']], :indentation => 3) # => "---\n- a\n-  - b\n"

# Dump an array to an IO with indentation set
Psych.dump(['a', ['b']], StringIO.new, :indentation => 3)



235
236
237
238
239
240
241
242
243
244
 
# File 'lib/psych.rb', line 235

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

  visitor = Psych::Visitors::YAMLTree.new options
  visitor << o
  visitor.tree.yaml io, options
end

.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"



252
253
254
255
256
257
258
 
# File 'lib/psych.rb', line 252

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

.libyaml_version ⇒ Object

Returns the version of libyaml being used



7
8
9
10
11
12
13
14
15
16
17
18
19
 
# File 'psych.c', line 7

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, filename = nil) ⇒ Object

Load yaml in to a Ruby data structure. If multiple documents are provided, the object contained in the first document will be returned. filename will be used in the exception message if any exception is raised while parsing.

Raises a Psych::SyntaxError when a YAML syntax error is detected.

Example:

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

begin
  Psych.load("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(foo.txt): found character that cannot start any token"
end



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

def self.load yaml, filename = nil
  result = parse(yaml, filename)
  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



296
297
298
 
# File 'lib/psych.rb', line 296

def self.load_file filename
  File.open(filename, 'r:bom|utf-8') { |f| self.load f, filename }
end

.load_stream(yaml, filename = nil) ⇒ Object

Load multiple documents given in yaml. Returns the parsed documents as a list. If a block is given, each document will be converted to ruby and passed to the block during parsing

Example:

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

list = []
Psych.load_stream("--- foo\n...\n--- bar\n...") do |ruby|
  list << ruby
end
list # => ['foo', 'bar']



283
284
285
286
287
288
289
290
291
 
# File 'lib/psych.rb', line 283

def self.load_stream yaml, filename = nil
  if block_given?
    parse_stream(yaml, filename) do |node|
      yield node.to_ruby
    end
  else
    parse_stream(yaml, filename).children.map { |child| child.to_ruby }
  end
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, filename = nil) ⇒ Object

Parse a YAML string in yaml. Returns the first object of a YAML AST. filename is used in the exception message if a Psych::SyntaxError is raised.

Raises a Psych::SyntaxError when a YAML syntax error is detected.

Example:

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

begin
  Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(foo.txt): found character that cannot start any token"
end

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



150
151
152
153
154
155
 
# File 'lib/psych.rb', line 150

def self.parse yaml, filename = nil
  parse_stream(yaml, filename) do |node|
    return node
  end
  false
end

.parse_file(filename) ⇒ Object

Parse a file at filename. Returns the YAML AST.

Raises a Psych::SyntaxError when a YAML syntax error is detected.



161
162
163
164
165
 
# File 'lib/psych.rb', line 161

def self.parse_file filename
  File.open filename, 'r:bom|utf-8' do |f|
    parse f, filename
  end
end

.parse_stream(yaml, filename = nil, &block) ⇒ 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. filename is used in the exception message if a Psych::SyntaxError is raised.

If a block is given, a Psych::Nodes::Document node will be yielded to the block as it's being parsed.

Raises a Psych::SyntaxError when a YAML syntax error is detected.

Example:

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

Psych.parse_stream("--- a\n--- b") do |node|
  node # => #<Psych::Nodes::Document:0x00>
end

begin
  Psych.parse_stream("--- `", "file.txt")
rescue Psych::SyntaxError => ex
  ex.file    # => 'file.txt'
  ex.message # => "(foo.txt): found character that cannot start any token"
end

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



200
201
202
203
204
205
206
207
208
209
 
# File 'lib/psych.rb', line 200

def self.parse_stream yaml, filename = nil, &block
  if block_given?
    parser = Psych::Parser.new(Handlers::DocumentStream.new(&block))
    parser.parse yaml, filename
  else
    parser = self.parser
    parser.parse yaml, filename
    parser.handler.root
  end
end

.parser ⇒ Object

Returns a default parser



169
170
171
 
# File 'lib/psych.rb', line 169

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 # :nodoc:
  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 



314
315
316
 
# File 'lib/psych.rb', line 314

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.



262
263
264
265
266
 
# File 'lib/psych.rb', line 262

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