rapidyaml 0.15.2

Parse and emit YAML, and do it fast. Python wrapper for the C++ library

Rapid YAML - Python package

Or ryml, for short. ryml is a C++ library to parse and emit YAML, and do it fast, on everything from x64 to bare-metal chips without operating system. This repo contains the rapidyaml python package, which was previously in the original repo (up to release 0.11.0).

This python wrapper exposes only the index-based low-level C++ API, which works with node indices and string views. This API is blazing fast, but you may find it hard to use: it does not build a python structure of dicts/seqs/scalars (that's up to you), and all the scalars are untyped strings. With that said, it is really fast, and once you have the tree you can still walk over the tree to create the native python structure.

Performance

Here are some results for a timeit benchmark comparing ryml against PyYaml and ruamel.yaml (and note you can use this script with your YAML files!). ryml parses quicker by generally 100x and up to 400x:

+----------------------------------------+-------+----------+----------+-----------+
| style_seqs_blck_outer1000_inner100.yml | count | time(ms) | avg(ms)  | avg(MB/s) |
+----------------------------------------+-------+----------+----------+-----------+
| parse:RuamelYamlParse                  |     1 | 4564.812 | 4564.812 |     0.173 |
| parse:PyYamlParse                      |     1 | 2815.426 | 2815.426 |     0.280 |
| parse:RymlParseInArena                 |    38 |  588.024 |   15.474 |    50.988 |
| parse:RymlParseInArenaReuse            |    38 |  466.997 |   12.289 |    64.202 |
| parse:RymlParseInPlace                 |    38 |  579.770 |   15.257 |    51.714 |
| parse:RymlParseInPlaceReuse            |    38 |  462.932 |   12.182 |    64.765 |
+----------------------------------------+-------+----------+----------+-----------+

(Note that the parse timings above are somewhat biased towards ryml, because it does not perform any type conversions in Python-land: return types are merely memoryviews to the source buffer, possibly copied to the tree's arena).

As for emitting, the improvement can be as high as 3000x:

+----------------------------------------+-------+-----------+-----------+-----------+
| style_maps_blck_outer1000_inner100.yml | count |  time(ms) |  avg(ms)  | avg(MB/s) |
+----------------------------------------+-------+-----------+-----------+-----------+
| emit_yaml:RuamelYamlEmit               |     1 | 18149.288 | 18149.288 |     0.054 |
| emit_yaml:PyYamlEmit                   |     1 |  2683.380 |  2683.380 |     0.365 |
| emit_yaml:RymlEmitToNewBuffer          |    88 |   861.726 |     9.792 |    99.976 |
| emit_yaml:RymlEmitReuse                |    88 |   437.931 |     4.976 |   196.725 |
+----------------------------------------+-------+-----------+-----------+-----------+

Examples

Parsing a file

Here's a quick example (this is a unit test at test/test_ex_read.py):

import ryml

def test_read_yaml():
    yaml = b"{HELLO: a, foo: b, bar: c, baz: d, seq: [0, 1, 2, 3]}"

    # ryml holds only views to the parsed yaml source (following the C++ library).
    #
    # parse_in_place() parses directly the input buffer,
    # so this requires the user to keep the input buffer
    # alive while using the tree.
    #
    # parse_in_arena() copies the input buffer to
    # an arena in the tree, then parses the copy.
    # This is safer, so let's use it here:
    tree = ryml.parse_in_arena(yaml)

    # The returned tree has the following structure:
    #
    #   [node 0] root, map
    #     ` [node 1] "HELLO": "a"
    #     ` [node 2] "foo": "b"
    #     ` [node 3] "bar": "c"
    #     ` [node 4] "baz": "d"
    #     ` [node 5] "seq":
    #         ` [node 6] "0"
    #         ` [node 7] "1"
    #         ` [node 8] "2"
    #         ` [node 9] "3"
    #
    # let's now do some assertions (keeping this structure in mind):
    assert tree.size() == 10
    assert tree.root_id() == 0
    assert tree.is_root(0)
    assert tree.is_map(0)
    assert tree.is_keyval(1)
    assert tree.is_seq(5)
    assert tree.is_val(6)
    # use bytes or str objects for queries
    assert tree.find_child(0, b"HELLO") == 1
    assert tree.find_child(0, "HELLO") == 1
    assert tree.find_child(0, b"foo") == 2
    assert tree.find_child(0, "foo") == 2
    assert tree.find_child(0, b"seq") == 5
    assert tree.find_child(0, "seq") == 5
    assert tree.key(1) == b"HELLO"
    assert tree.val(1) == b"a"
    assert tree.key(2) == b"foo"
    assert tree.val(2) == b"b"
    assert tree.find_child(0, b"seq") == 5
    assert tree.find_child(0, "seq") == 5
    # hierarchy:
    assert tree.first_child(0) == 1
    assert tree.last_child(0) == 5
    assert tree.next_sibling(1) == 2
    assert tree.first_sibling(5) == 1
    assert tree.last_sibling(1) == 5
    assert tree.first_child(5) == 6
    assert tree.last_child(5) == 9
    # to loop over children:
    expected = [b"0", b"1", b"2", b"3"]
    for i, ch in enumerate(ryml.children(tree, 5)):
        assert tree.val(ch) == expected[i]
    # to loop over siblings:
    expected = [b"HELLO", b"foo", b"bar", b"baz", b"seq"]
    for i, sib in enumerate(ryml.siblings(tree, 5)):
        assert tree.key(sib) == expected[i]
    # to walk over all elements
    visited = [False] * tree.size()
    for node_id, indentation_level in ryml.walk(tree):
        visited[node_id] = True
    assert False not in visited
    # NOTE about encoding!
    k = tree.key(5)
    assert isinstance(k, memoryview)
    #print(k)  # '<memory at 0x7f80d5b93f48>'
    assert k == b"seq"               # ok, as expected
    assert k != "seq"                # not ok - NOTE THIS!
    assert str(k) != "seq"           # not ok
    assert str(k, "utf8") == "seq"   # ok again

Creating and emitting a tree

Here are some examples on how to create trees programatically (this is a unit test at test/test_ex_write.py):

import ryml


# all the tests below create this tree
expected_yaml = '{HELLO: a,foo: b,bar: c,baz: d,seq: [0,1,2,3]}'
expected_json = '{"HELLO": "a","foo": "b","bar": "c","baz": "d","seq": [0,1,2,3]}'


# helper to create map children nodes
def _append_keyval(tree: ryml.Tree, node_id: int, key, val, flags=0):
    child_id = tree.append_child(node_id)
    tree.to_keyval(child_id, key, val, flags)
    return child_id


# helper to create seq children nodes
def _append_val(tree: ryml.Tree, node_id: int, val, flags=0):
    child_id = tree.append_child(node_id)
    tree.to_val(child_id, val, flags)
    return child_id


def test_create_tree():
    tree = ryml.Tree()
    root_id = tree.root_id()
    tree.to_map(root_id, ryml.FLOW_SL) # set the root node as a map,
                                       # with FLOW_SL style (flow, single line)
    _append_keyval(tree, root_id, "HELLO", "a")
    _append_keyval(tree, root_id, "foo", "b")
    _append_keyval(tree, root_id, "bar", "c")
    _append_keyval(tree, root_id, "baz", "d")
    seq_id = tree.append_child(root_id)
    tree.to_seq(seq_id, "seq", ryml.FLOW_SL)  # append a sequence
    _append_val(tree, seq_id, "0")
    _append_val(tree, seq_id, "1")
    _append_val(tree, seq_id, "2")
    _append_val(tree, seq_id, "3")
    # check that this tree is emitted as expected
    _check_emits(tree)


# BEWARE! The tree is pointing at the memory of the scalars!
#
# If you are using dynamic strings for scalars, you must be sure to
# hold onto them while using the tree!
#
# Because explicitly managing lifetimes is generally hard or
# cumbersome to do in python, ryml provides you a tree.to_arena()
# helper to do this: it copies the scalar to the tree's arena, which
# will fix any lifetime issues.
#
# Here's an example:
def test_create_tree_dynamic():
    # let's now programmatically create the same tree as above:
    tree = ryml.Tree()
    root_id = tree.root_id()
    tree.to_map(root_id, ryml.FLOW_SL) # set the root node as a map,
                                       # with FLOW_SL style (flow, single line)
    # utility function to create a dynamic string and store it in the tree:
    def ds(s: str):
        # make a dynamic copy (using f-string to force creation a
        # different string object)
        dyn = f"_{s}_"[1:-1]
        # ...serialize the copy in the tree's arena
        saved = tree.to_arena(dyn)
        return saved
    # now we use ds() with each scalar, making it safer
    _append_keyval(tree, root_id, ds("HELLO"), ds("a"))
    _append_keyval(tree, root_id, ds("foo"), ds("b"))
    _append_keyval(tree, root_id, ds("bar"), ds("c"))
    _append_keyval(tree, root_id, ds("baz"), ds("d"))
    seq_id = tree.append_child(root_id)
    tree.to_seq(seq_id, ds("seq"), ryml.FLOW_SL)  # append a sequence
    _append_val(tree, seq_id, ds("0"))
    _append_val(tree, seq_id, ds("1"))
    _append_val(tree, seq_id, ds("2"))
    _append_val(tree, seq_id, ds("3"))
    # check that this tree is emitted as expected
    _check_emits(tree)


# But note you don't need to use tree.to_arena(); you can save the
# dynamic scalars for example by keeping them in a tree. But then you
# must take care of the lifetimes!
#
# Here's an example:
def test_create_tree_dynamic_explicit_save():
    # let's now programmatically create the same tree as above:
    tree = ryml.Tree()
    root_id = tree.root_id()
    tree.to_map(root_id, ryml.FLOW_SL) # set the root node as a map,
                                       # with FLOW_SL style (flow, single line)
    # this time we'll use a list to save the scalars. It works because
    # both `tree` and `saved_scalars` are defined and used in the same
    # scope. But it would fail if `saved_scalars` went out of scope
    # before ending the use of `tree`, eg if tree was returned from
    # this function but `saved_scalars` were not.
    saved_scalars = []
    # utility function to create a dynamic string and store it:
    def ds(s: str):
        # make a dynamic copy (using f-string to force creation a
        # different string object)
        dyn = f"_{s}_"[1:-1]
        # save the string in the list
        saved_scalars.append(dyn)
        return dyn
    # now we use ds() with each scalar, making it safer
    _append_keyval(tree, root_id, ds("HELLO"), ds("a"))
    _append_keyval(tree, root_id, ds("foo"), ds("b"))
    _append_keyval(tree, root_id, ds("bar"), ds("c"))
    _append_keyval(tree, root_id, ds("baz"), ds("d"))
    seq_id = tree.append_child(root_id)
    tree.to_seq(seq_id, ds("seq"), ryml.FLOW_SL)  # append a sequence
    _append_val(tree, seq_id, ds("0"))
    _append_val(tree, seq_id, ds("1"))
    _append_val(tree, seq_id, ds("2"))
    _append_val(tree, seq_id, ds("3"))
    # check that this tree is emitted as expected
    _check_emits(tree)


def test_create_tree_bytes():
    # ryml also works with bytes scalars
    tree = ryml.Tree()
    root_id = tree.root_id()
    tree.to_map(root_id, ryml.FLOW_SL) # set the root node as a map,
                                       # with FLOW_SL style (flow, single line)
    _append_keyval(tree, root_id, b"HELLO", b"a")
    _append_keyval(tree, root_id, b"foo", b"b")
    _append_keyval(tree, root_id, b"bar", b"c")
    _append_keyval(tree, root_id, b"baz", b"d")
    seq_id = tree.append_child(root_id)
    tree.to_seq(seq_id, b"seq", ryml.FLOW_SL)  # append a sequence
    _append_val(tree, seq_id, b"0")
    _append_val(tree, seq_id, b"1")
    _append_val(tree, seq_id, b"2")
    _append_val(tree, seq_id, b"3")
    # check that this tree is emitted as expected
    _check_emits(tree)


def test_create_tree_memoryview():
    # ryml also works with memoryview scalars
    tree = ryml.Tree()
    root_id = tree.root_id()
    tree.to_map(root_id, ryml.FLOW_SL) # set the root node as a map,
                                       # with FLOW_SL style (flow, single line)
    def s(scalar: bytes):
        return memoryview(scalar)
    _append_keyval(tree, root_id, s(b"HELLO"), s(b"a"))
    _append_keyval(tree, root_id, s(b"foo"), s(b"b"))
    _append_keyval(tree, root_id, s(b"bar"), s(b"c"))
    _append_keyval(tree, root_id, s(b"baz"), s(b"d"))
    seq_id = tree.append_child(root_id)
    tree.to_seq(seq_id, s(b"seq"), ryml.FLOW_SL)  # append a sequence
    _append_val(tree, seq_id, s(b"0"))
    _append_val(tree, seq_id, s(b"1"))
    _append_val(tree, seq_id, s(b"2"))
    _append_val(tree, seq_id, s(b"3"))
    # check that this tree is emitted as expected
    _check_emits(tree)


# this function shows several different ways of emitting from an
# existing tree (and tests that the results are as expected).
def _check_emits(tree: ryml.Tree):
    # emit_yaml() and emit_json() return a str object
    out_yaml = ryml.emit_yaml(tree)
    out_json = ryml.emit_json(tree)
    assert isinstance(out_yaml, str)
    assert isinstance(out_json, str)
    assert out_yaml == expected_yaml
    assert out_json == expected_json
    # if it is really important, you can emit to existing buffers:
    len_yaml = ryml.compute_yaml_length(tree) #
    len_json = ryml.compute_json_length(tree)
    buf_yaml = bytearray(len_yaml)
    buf_json = bytearray(len_json)
    out_yaml = ryml.emit_yaml_in_place(tree, buf_yaml)
    out_json = ryml.emit_json_in_place(tree, buf_json)
    assert isinstance(out_yaml, memoryview)
    assert isinstance(out_json, memoryview)
    assert out_yaml.tobytes().decode('utf8') == expected_yaml
    assert out_json.tobytes().decode('utf8') == expected_json

---

License

ryml is permissively licensed under the MIT license.