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Psych is a YAML parser and emitter. Psych leverages libyaml [Home page: pyyaml.org/wiki/LibYAML] or [Git repo: github.com/zerotao/libyaml] for its 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.
# Parse some YAML Psych.load("--- foo") # => "foo" # Emit some YAML Psych.dump("foo") # => "--- foo\n...\n" { :a => 'b'}.to_yaml # => "---\n:a: b\n"
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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.
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.
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 ::parse_stream, Psych::Nodes, and Psych::Nodes::Node for more information on dealing with YAML syntax trees.
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 ::load
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.
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.
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.
The high level emitter has the easiest interface. Psych simply takes a Ruby data structure and converts it to a YAML document. See ::dump for more information on dumping a Ruby data structure.
The version of libyaml Psych is using
The version is Psych you're using
# File psych/lib/psych/deprecated.rb, line 48 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
# File psych/lib/psych/deprecated.rb, line 41 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
# File psych/lib/psych/deprecated.rb, line 34 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 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)
# File psych/lib/psych.rb, line 237 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 a list of objects as separate documents to a document stream.
Example:
Psych.dump_stream("foo\n ", {}) # => "--- ! \"foo\\n \"\n--- {}\n"
# File psych/lib/psych.rb, line 254 def self.dump_stream *objects visitor = Psych::Visitors::YAMLTree.new {} objects.each do |o| visitor << o end visitor.tree.yaml end
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
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 # => "(file.txt): found character that cannot start any token" end
# File psych/lib/psych.rb, line 128 def self.load yaml, filename = nil result = parse(yaml, filename) result ? result.to_ruby : result end
This method is deprecated, use ::load_stream instead.
# File psych/lib/psych/deprecated.rb, line 25 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 the document contained in filename
. Returns the yaml
contained in filename
as a ruby object
# File psych/lib/psych.rb, line 298 def self.load_file filename File.open(filename, 'r:bom|utf-8') { |f| self.load f, filename } end
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']
# File psych/lib/psych.rb, line 285 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
# File psych/lib/psych/deprecated.rb, line 71 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 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 # => "(file.txt): found character that cannot start any token" end
See Psych::Nodes for more information about YAML AST.
# File psych/lib/psych.rb, line 152 def self.parse yaml, filename = nil parse_stream(yaml, filename) do |node| return node end false end
Parse a file at filename
. Returns the YAML AST.
Raises a Psych::SyntaxError when a YAML syntax error is detected.
# File psych/lib/psych.rb, line 163 def self.parse_file filename File.open filename, 'r:bom|utf-8' do |f| parse f, filename end end
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 # => "(file.txt): found character that cannot start any token" end
See Psych::Nodes for more information about YAML AST.
# File psych/lib/psych.rb, line 202 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
Returns a default parser
# File psych/lib/psych.rb, line 171 def self.parser Psych::Parser.new(TreeBuilder.new) end
# File psych/lib/psych/deprecated.rb, line 61 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
# File psych/lib/psych/deprecated.rb, line 55 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
Dump Ruby object o
to a JSON
string.
# File psych/lib/psych.rb, line 264 def self.to_json o visitor = Psych::Visitors::JSONTree.new visitor << o visitor.tree.yaml end