Module: Psych
Overview
Psych
is a YAML parser and emitter. Psych
leverages libyaml [Home page: pyyaml.org/wiki/LibYAML] or [HG repo: bitbucket.org/xi/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.
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.
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.
High-level API
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 .load
Reading from a string
Psych.load("--- a") # => 'a'
Psych.load("---\n - a\n - b") # => ['a', 'b']
Reading from a file
Psych.load_file("database.yml")
Exception handling
begin
# The second argument changes only the exception contents
Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
ex.file # => 'file.txt'
ex. # => "(file.txt): found character that cannot start any token"
end
Emitting
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.
Writing to a string
# 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)
Writing to a file
Currently there is no direct API for dumping Ruby structure to file:
File.open('database.yml', 'w') do |file|
file.write(Psych.dump(['a', 'b']))
end
Mid-level API
Parsing
Psych
provides access to an AST produced from parsing a YAML document. This tree is built using the Parser and TreeBuilder. The AST can be examined and manipulated freely. Please see .parse_stream, Nodes, and ::Psych::Nodes::Node for more information on dealing with YAML syntax trees.
Reading from a string
# Returns Psych::Nodes::Stream
Psych.parse_stream("---\n - a\n - b")
# Returns Psych::Nodes::Document
Psych.parse("---\n - a\n - b")
Reading from a file
# Returns Psych::Nodes::Stream
Psych.parse_stream(File.read('database.yml'))
# Returns Psych::Nodes::Document
Psych.parse_file('database.yml')
Exception handling
begin
# The second argument changes only the exception contents
Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
ex.file # => 'file.txt'
ex. # => "(file.txt): found character that cannot start any token"
end
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 Nodes, ::Psych::Nodes::Node, and TreeBuilder for more information on building a YAML AST.
Writing to a string
# We need Psych::Nodes::Stream (not Psych::Nodes::Document)
stream = Psych.parse_stream("---\n - a\n - b")
stream.to_yaml # => "---\n- a\n- b\n"
Writing to a file
# We need Psych::Nodes::Stream (not Psych::Nodes::Document)
stream = Psych.parse_stream(File.read('database.yml'))
File.open('database.yml', 'w') do |file|
file.write(stream.to_yaml)
end
Low-level API
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 Parser for more information on using the event based parser.
Reading to ::Psych::Nodes::Stream structure
parser = Psych::Parser.new(TreeBuilder.new) # => #<Psych::Parser>
parser = Psych.parser # it's an alias for the above
parser.parse("---\n - a\n - b") # => #<Psych::Parser>
parser.handler # => #<Psych::TreeBuilder>
parser.handler.root # => #<Psych::Nodes::Stream>
Receiving an events stream
parser = Psych::Parser.new(Psych::Handlers::Recorder.new)
parser.parse("---\n - a\n - b")
parser.events # => [list of [event, args] lists]
# event is one of: Psych::Handler::EVENTS
# args are the arguments passed to the event
Emitting
The lowest level emitter is an event based system. Events are sent to a 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 Emitter for more information.
Writing to a Ruby structure
Psych.parser.parse("--- a") # => #<Psych::Parser>
parser.handler.first # => #<Psych::Nodes::Stream>
parser.handler.first.to_ruby # => ["a"]
parser.handler.root.first # => #<Psych::Nodes::Document>
parser.handler.root.first.to_ruby # => "a"
# You can instantiate an Emitter manually
Psych::Visitors::ToRuby.new.accept(parser.handler.root.first)
# => "a"
Constant Summary
-
DEFAULT_SNAKEYAML_VERSION =
# File 'ext/psych/lib/psych/versions.rb', line 3'1.14'.freeze
-
LIBYAML_VERSION =
The version of libyaml
Psych
is usingPsych.libyaml_version.join '.'
-
VERSION =
The version is
Psych
you're using'2.1.0'
Class Attribute Summary
- .domain_types rw
- .dump_tags rw
- .load_tags rw
Class Method Summary
- .add_builtin_type(type_tag, &block)
- .add_domain_type(domain, type_tag, &block)
- .add_private_type(type_tag, &block)
- .add_ruby_type(type_tag, &block)
- .add_tag(tag, klass)
- .detect_implicit(thing)
-
.dump(o) ⇒ string of yaml
Dump Ruby object
o
to a YAML string. -
.dump_stream(*objects)
Dump a list of objects as separate documents to a document stream.
-
.libyaml_version
Returns the version of libyaml being used.
-
.load(yaml, filename = nil, fallback = false)
Load
yaml
in to a Ruby data structure. -
.load_documents(yaml, &block)
This method is deprecated, use .load_stream instead.
-
.load_file(filename, fallback = false)
Load the document contained in
filename
. -
.load_stream(yaml, filename = nil)
Load multiple documents given in
yaml
. - .object_maker(klass, hash)
-
.parse(yaml, filename = nil, fallback = false)
Parse a YAML string in
yaml
. -
.parse_file(filename)
Parse a file at
filename
. -
.parse_stream(yaml, filename = nil, &block)
Parse a YAML string in
yaml
. -
.parser
Returns a default parser.
- .read_type_class(type, reference)
- .remove_type(type_tag)
-
.safe_load(yaml, whitelist_classes = [], whitelist_symbols = [], aliases = false, filename = nil)
Safely load the yaml string in
yaml
. - .tagurize(thing)
-
.to_json(object)
Dump Ruby
object
to a JSON string.
Class Attribute Details
.domain_types (rw)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 507
attr_accessor :domain_types
.dump_tags (rw)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 506
attr_accessor :
.load_tags (rw)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 505
attr_accessor :
Class Method Details
.add_builtin_type(type_tag, &block)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 487
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)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 481
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)
[ GitHub ]# File 'ext/psych/lib/psych/deprecated.rb', line 50
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)
[ GitHub ]# File 'ext/psych/lib/psych/deprecated.rb', line 43
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)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 499
def self.add_tag tag, klass @load_tags[tag] = klass.name @dump_tags[klass] = tag end
.detect_implicit(thing)
[ GitHub ]# File 'ext/psych/lib/psych/deprecated.rb', line 35
def self.detect_implicit thing warn "#{caller[0]}: detect_implicit is deprecated" if $VERBOSE return '' unless String === thing return 'null' if '' == thing ss = ScalarScanner.new(ClassLoader.new) ss.tokenize(thing).class.name.downcase end
.dump(o) ⇒ string
of
yaml
.dump(o, options) ⇒ string
of
yaml
.dump(o, io) ⇒ io
object
passed
in
.dump(o, io, options) ⇒ io
object
passed
in
string
of
yaml
.dump(o, options) ⇒ string
of
yaml
.dump(o, io) ⇒ io
object
passed
in
.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)
.dump_stream(*objects)
Dump a list of objects as separate documents to a document stream.
Example:
Psych.dump_stream("foo\n ", {}) # => "--- ! \"foo\\n \"\n--- {}\n"
.libyaml_version
Returns the version of libyaml being used
.load(yaml, filename = nil, fallback = false)
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. # => "(file.txt): found character that cannot start any token"
end
# File 'ext/psych/lib/psych.rb', line 253
def self.load yaml, filename = nil, fallback = false result = parse(yaml, filename, fallback) result ? result.to_ruby : result end
.load_documents(yaml, &block)
This method is deprecated, use .load_stream instead.
# File 'ext/psych/lib/psych/deprecated.rb', line 26
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, fallback = false)
Load the document contained in filename
. Returns the yaml contained in filename
as a Ruby object, or if the file is empty, it returns the specified default return value, which defaults to an empty Hash
.load_stream(yaml, filename = nil)
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 'ext/psych/lib/psych.rb', line 459
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)
[ GitHub ]# File 'ext/psych/lib/psych/deprecated.rb', line 73
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, fallback = false)
Parse a YAML string in yaml
. Returns the ::Psych::Nodes::Document. 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::Document:0x00>
begin
Psych.parse("--- `", "file.txt")
rescue Psych::SyntaxError => ex
ex.file # => 'file.txt'
ex. # => "(file.txt): found character that cannot start any token"
end
See ::Psych::Nodes for more information about YAML AST.
# File 'ext/psych/lib/psych.rb', line 326
def self.parse yaml, filename = nil, fallback = false parse_stream(yaml, filename) do |node| return node end fallback end
.parse_file(filename)
Parse a file at filename
. Returns the ::Psych::Nodes::Document.
Raises a ::Psych::SyntaxError when a YAML syntax error is detected.
# File 'ext/psych/lib/psych.rb', line 337
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)
Parse a YAML string in yaml
. Returns the ::Psych::Nodes::Stream. 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. # => "(file.txt): found character that cannot start any token"
end
See ::Psych::Nodes for more information about YAML AST.
.parser
Returns a default parser
# File 'ext/psych/lib/psych.rb', line 345
def self.parser Psych::Parser.new(TreeBuilder.new) end
.read_type_class(type, reference)
[ GitHub ]# File 'ext/psych/lib/psych/deprecated.rb', line 63
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)
[ GitHub ]# File 'ext/psych/lib/psych.rb', line 493
def self.remove_type type_tag @domain_types.delete type_tag end
.safe_load(yaml, whitelist_classes = [], whitelist_symbols = [], aliases = false, filename = nil)
Safely load the yaml string in yaml
. By default, only the following classes are allowed to be deserialized:
-
TrueClass
-
FalseClass
-
NilClass
-
Numeric
-
String
-
Array
-
Hash
Recursive data structures are not allowed by default. Arbitrary classes can be allowed by adding those classes to the whitelist
. They are additive. For example, to allow Date deserialization:
Psych.safe_load(yaml, [Date])
Now the Date class can be loaded in addition to the classes listed above.
Aliases can be explicitly allowed by changing the aliases
parameter. For example:
x = []
x << x
yaml = Psych.dump x
Psych.safe_load yaml # => raises an exception
Psych.safe_load yaml, [], [], true # => loads the aliases
A ::Psych::DisallowedClass exception will be raised if the yaml contains a class that isn't in the whitelist.
A ::Psych::BadAlias exception will be raised if the yaml contains aliases but the aliases
parameter is set to false.
# File 'ext/psych/lib/psych.rb', line 292
def self.safe_load yaml, whitelist_classes = [], whitelist_symbols = [], aliases = false, filename = nil result = parse(yaml, filename) return unless result class_loader = ClassLoader::Restricted.new(whitelist_classes.map(&:to_s), whitelist_symbols.map(&:to_s)) scanner = ScalarScanner.new class_loader if aliases visitor = Visitors::ToRuby.new scanner, class_loader else visitor = Visitors::NoAliasRuby.new scanner, class_loader end visitor.accept result end
.tagurize(thing)
[ GitHub ]# File 'ext/psych/lib/psych/deprecated.rb', line 57
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(object)
Dump Ruby object
to a ::Psych::JSON string.