diff --git a/dvc/dependency/param.py b/dvc/dependency/param.py
--- a/dvc/dependency/param.py
+++ b/dvc/dependency/param.py
@@ -2,12 +2,11 @@
 from collections import defaultdict
 
 import dpath.util
-import toml
-import yaml
 from voluptuous import Any
 
 from dvc.dependency.local import LocalDependency
 from dvc.exceptions import DvcException
+from dvc.utils.serialize import PARSERS, ParseError
 
 
 class MissingParamsError(DvcException):
@@ -22,8 +21,6 @@ class ParamsDependency(LocalDependency):
     PARAM_PARAMS = "params"
     PARAM_SCHEMA = {PARAM_PARAMS: Any(dict, list, None)}
     DEFAULT_PARAMS_FILE = "params.yaml"
-    PARAMS_FILE_LOADERS = defaultdict(lambda: yaml.safe_load)
-    PARAMS_FILE_LOADERS.update({".toml": toml.load})
 
     def __init__(self, stage, path, params):
         info = {}
@@ -88,12 +85,12 @@ def read_params(self):
         if not self.exists:
             return {}
 
+        suffix = self.path_info.suffix.lower()
+        parser = PARSERS[suffix]
         with self.repo.tree.open(self.path_info, "r") as fobj:
             try:
-                config = self.PARAMS_FILE_LOADERS[
-                    self.path_info.suffix.lower()
-                ](fobj)
-            except (yaml.YAMLError, toml.TomlDecodeError) as exc:
+                config = parser(fobj.read(), self.path_info)
+            except ParseError as exc:
                 raise BadParamFileError(
                     f"Unable to read parameters from '{self}'"
                 ) from exc
diff --git a/dvc/exceptions.py b/dvc/exceptions.py
--- a/dvc/exceptions.py
+++ b/dvc/exceptions.py
@@ -182,22 +182,6 @@ def __init__(self):
         )
 
 
-class YAMLFileCorruptedError(DvcException):
-    def __init__(self, path):
-        path = relpath(path)
-        super().__init__(
-            f"unable to read: '{path}', YAML file structure is corrupted"
-        )
-
-
-class TOMLFileCorruptedError(DvcException):
-    def __init__(self, path):
-        path = relpath(path)
-        super().__init__(
-            f"unable to read: '{path}', TOML file structure is corrupted"
-        )
-
-
 class RecursiveAddingWhileUsingFilename(DvcException):
     def __init__(self):
         super().__init__(
diff --git a/dvc/repo/metrics/show.py b/dvc/repo/metrics/show.py
--- a/dvc/repo/metrics/show.py
+++ b/dvc/repo/metrics/show.py
@@ -1,12 +1,11 @@
 import logging
 import os
 
-import yaml
-
 from dvc.exceptions import NoMetricsError
 from dvc.path_info import PathInfo
 from dvc.repo import locked
 from dvc.repo.tree import RepoTree
+from dvc.utils.serialize import YAMLFileCorruptedError, parse_yaml
 
 logger = logging.getLogger(__name__)
 
@@ -72,8 +71,8 @@ def _read_metrics(repo, metrics, rev):
         try:
             with tree.open(metric, "r") as fobj:
                 # NOTE this also supports JSON
-                val = yaml.safe_load(fobj)
-        except (FileNotFoundError, yaml.YAMLError):
+                val = parse_yaml(fobj.read(), metric)
+        except (FileNotFoundError, YAMLFileCorruptedError):
             logger.debug(
                 "failed to read '%s' on '%s'", metric, rev, exc_info=True
             )
diff --git a/dvc/repo/params/show.py b/dvc/repo/params/show.py
--- a/dvc/repo/params/show.py
+++ b/dvc/repo/params/show.py
@@ -1,12 +1,10 @@
 import logging
 
-import toml
-import yaml
-
 from dvc.dependency.param import ParamsDependency
 from dvc.exceptions import DvcException
 from dvc.path_info import PathInfo
 from dvc.repo import locked
+from dvc.utils.serialize import PARSERS, ParseError
 
 logger = logging.getLogger(__name__)
 
@@ -33,12 +31,12 @@ def _read_params(repo, configs, rev):
         if not repo.tree.exists(config):
             continue
 
+        suffix = config.suffix.lower()
+        parser = PARSERS[suffix]
         with repo.tree.open(config, "r") as fobj:
             try:
-                res[str(config)] = ParamsDependency.PARAMS_FILE_LOADERS[
-                    config.suffix.lower()
-                ](fobj)
-            except (yaml.YAMLError, toml.TomlDecodeError):
+                res[str(config)] = parser(fobj.read(), config)
+            except ParseError:
                 logger.debug(
                     "failed to read '%s' on '%s'", config, rev, exc_info=True
                 )
diff --git a/dvc/repo/plots/data.py b/dvc/repo/plots/data.py
--- a/dvc/repo/plots/data.py
+++ b/dvc/repo/plots/data.py
@@ -5,9 +5,8 @@
 from collections import OrderedDict
 from copy import copy
 
-import yaml
 from funcy import first
-from yaml import SafeLoader
+from ruamel.yaml import YAML
 
 from dvc.exceptions import DvcException
 
@@ -208,18 +207,7 @@ def raw(self, header=True, **kwargs):  # pylint: disable=arguments-differ
 
 class YAMLPlotData(PlotData):
     def raw(self, **kwargs):
-        class OrderedLoader(SafeLoader):
-            pass
-
-        def construct_mapping(loader, node):
-            loader.flatten_mapping(node)
-            return OrderedDict(loader.construct_pairs(node))
-
-        OrderedLoader.add_constructor(
-            yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG, construct_mapping
-        )
-
-        return yaml.load(self.content, OrderedLoader)
+        return YAML().load(self.content)
 
     def _processors(self):
         parent_processors = super()._processors()
diff --git a/dvc/repo/reproduce.py b/dvc/repo/reproduce.py
--- a/dvc/repo/reproduce.py
+++ b/dvc/repo/reproduce.py
@@ -120,9 +120,10 @@ def reproduce(
 
 def _parse_params(path_params):
     from flatten_json import unflatten
-    from yaml import YAMLError, safe_load
+    from ruamel.yaml import YAMLError
 
     from dvc.dependency.param import ParamsDependency
+    from dvc.utils.serialize import loads_yaml
 
     ret = {}
     for path_param in path_params:
@@ -133,7 +134,7 @@ def _parse_params(path_params):
             try:
                 # interpret value strings using YAML rules
                 key, value = param_str.split("=")
-                params[key] = safe_load(value)
+                params[key] = loads_yaml(value)
             except (ValueError, YAMLError):
                 raise InvalidArgumentError(
                     f"Invalid param/value pair '{param_str}'"
diff --git a/dvc/scm/git.py b/dvc/scm/git.py
--- a/dvc/scm/git.py
+++ b/dvc/scm/git.py
@@ -5,7 +5,6 @@
 import shlex
 from functools import partial
 
-import yaml
 from funcy import cached_property
 from pathspec.patterns import GitWildMatchPattern
 
@@ -20,6 +19,7 @@
 )
 from dvc.utils import fix_env, is_binary, relpath
 from dvc.utils.fs import path_isin
+from dvc.utils.serialize import dump_yaml, load_yaml
 
 logger = logging.getLogger(__name__)
 
@@ -316,11 +316,7 @@ def install(self, use_pre_commit_tool=False):
             return
 
         config_path = os.path.join(self.root_dir, ".pre-commit-config.yaml")
-
-        config = {}
-        if os.path.exists(config_path):
-            with open(config_path) as fobj:
-                config = yaml.safe_load(fobj)
+        config = load_yaml(config_path) if os.path.exists(config_path) else {}
 
         entry = {
             "repo": "https://github.com/iterative/dvc",
@@ -349,8 +345,7 @@ def install(self, use_pre_commit_tool=False):
             return
 
         config["repos"].append(entry)
-        with open(config_path, "w+") as fobj:
-            yaml.dump(config, fobj)
+        dump_yaml(config_path, config)
 
     def cleanup_ignores(self):
         for path in self.ignored_paths:
diff --git a/dvc/stage/cache.py b/dvc/stage/cache.py
--- a/dvc/stage/cache.py
+++ b/dvc/stage/cache.py
@@ -2,7 +2,6 @@
 import os
 from contextlib import contextmanager
 
-import yaml
 from funcy import first
 from voluptuous import Invalid
 
@@ -10,7 +9,7 @@
 from dvc.schema import COMPILED_LOCK_FILE_STAGE_SCHEMA
 from dvc.utils import dict_sha256, relpath
 from dvc.utils.fs import makedirs
-from dvc.utils.serialize import dump_yaml
+from dvc.utils.serialize import YAMLFileCorruptedError, dump_yaml, load_yaml
 
 from .loader import StageLoader
 from .serialize import to_single_stage_lockfile
@@ -54,11 +53,10 @@ def _load_cache(self, key, value):
         path = self._get_cache_path(key, value)
 
         try:
-            with open(path) as fobj:
-                return COMPILED_LOCK_FILE_STAGE_SCHEMA(yaml.safe_load(fobj))
+            return COMPILED_LOCK_FILE_STAGE_SCHEMA(load_yaml(path))
         except FileNotFoundError:
             return None
-        except (yaml.error.YAMLError, Invalid):
+        except (YAMLFileCorruptedError, Invalid):
             logger.warning("corrupted cache file '%s'.", relpath(path))
             os.unlink(path)
             return None
diff --git a/dvc/utils/__init__.py b/dvc/utils/__init__.py
--- a/dvc/utils/__init__.py
+++ b/dvc/utils/__init__.py
@@ -1,7 +1,6 @@
 """Helpers for other modules."""
 
 import hashlib
-import io
 import json
 import logging
 import math
@@ -12,7 +11,6 @@
 
 import colorama
 import nanotime
-from ruamel.yaml import YAML
 from shortuuid import uuid
 
 logger = logging.getLogger(__name__)
@@ -237,18 +235,6 @@ def current_timestamp():
     return int(nanotime.timestamp(time.time()))
 
 
-def from_yaml_string(s):
-    return YAML().load(io.StringIO(s))
-
-
-def to_yaml_string(data):
-    stream = io.StringIO()
-    yaml = YAML()
-    yaml.default_flow_style = False
-    yaml.dump(data, stream)
-    return stream.getvalue()
-
-
 def colorize(message, color=None):
     """Returns a message in a specified color."""
     if not color:
diff --git a/dvc/utils/serialize/__init__.py b/dvc/utils/serialize/__init__.py
--- a/dvc/utils/serialize/__init__.py
+++ b/dvc/utils/serialize/__init__.py
@@ -1,2 +1,8 @@
+from collections import defaultdict
+
+from ._common import *  # noqa, pylint: disable=wildcard-import
 from ._toml import *  # noqa, pylint: disable=wildcard-import
 from ._yaml import *  # noqa, pylint: disable=wildcard-import
+
+PARSERS = defaultdict(lambda: parse_yaml)  # noqa: F405
+PARSERS.update({".toml": parse_toml})  # noqa: F405
diff --git a/dvc/utils/serialize/_common.py b/dvc/utils/serialize/_common.py
new file mode 100644
--- /dev/null
+++ b/dvc/utils/serialize/_common.py
@@ -0,0 +1,12 @@
+"""Common utilities for serialize."""
+
+from dvc.exceptions import DvcException
+from dvc.utils import relpath
+
+
+class ParseError(DvcException):
+    """Errors while parsing files"""
+
+    def __init__(self, path, message):
+        path = relpath(path)
+        super().__init__(f"unable to read: '{path}', {message}")
diff --git a/dvc/utils/serialize/_toml.py b/dvc/utils/serialize/_toml.py
--- a/dvc/utils/serialize/_toml.py
+++ b/dvc/utils/serialize/_toml.py
@@ -1,6 +1,17 @@
 import toml
+from funcy import reraise
 
-from dvc.exceptions import TOMLFileCorruptedError
+from ._common import ParseError
+
+
+class TOMLFileCorruptedError(ParseError):
+    def __init__(self, path):
+        super().__init__(path, "TOML file structure is corrupted")
+
+
+def parse_toml(text, path, decoder=None):
+    with reraise(toml.TomlDecodeError, TOMLFileCorruptedError(path)):
+        return toml.loads(text, decoder=decoder)
 
 
 def parse_toml_for_update(text, path):
@@ -10,12 +21,10 @@ def parse_toml_for_update(text, path):
     keys may be re-ordered between load/dump, but this function will at
     least preserve comments.
     """
-    try:
-        return toml.loads(text, decoder=toml.TomlPreserveCommentDecoder())
-    except toml.TomlDecodeError as exc:
-        raise TOMLFileCorruptedError(path) from exc
+    decoder = toml.TomlPreserveCommentDecoder()
+    return parse_toml(text, path, decoder=decoder)
 
 
 def dump_toml(path, data):
-    with open(path, "w", encoding="utf-8") as fobj:
+    with open(path, "w+", encoding="utf-8") as fobj:
         toml.dump(data, fobj, encoder=toml.TomlPreserveCommentEncoder())
diff --git a/dvc/utils/serialize/_yaml.py b/dvc/utils/serialize/_yaml.py
--- a/dvc/utils/serialize/_yaml.py
+++ b/dvc/utils/serialize/_yaml.py
@@ -1,14 +1,16 @@
+import io
 from collections import OrderedDict
 
+from funcy import reraise
 from ruamel.yaml import YAML
 from ruamel.yaml.error import YAMLError
 
-from dvc.exceptions import YAMLFileCorruptedError
+from ._common import ParseError
 
-try:
-    from yaml import CSafeLoader as SafeLoader
-except ImportError:
-    from yaml import SafeLoader
+
+class YAMLFileCorruptedError(ParseError):
+    def __init__(self, path):
+        super().__init__(path, "YAML file structure is corrupted")
 
 
 def load_yaml(path):
@@ -16,13 +18,10 @@ def load_yaml(path):
         return parse_yaml(fd.read(), path)
 
 
-def parse_yaml(text, path):
-    try:
-        import yaml
-
-        return yaml.load(text, Loader=SafeLoader) or {}
-    except yaml.error.YAMLError as exc:
-        raise YAMLFileCorruptedError(path) from exc
+def parse_yaml(text, path, typ="safe"):
+    yaml = YAML(typ=typ)
+    with reraise(YAMLError, YAMLFileCorruptedError(path)):
+        return yaml.load(text) or {}
 
 
 def parse_yaml_for_update(text, path):
@@ -34,20 +33,30 @@ def parse_yaml_for_update(text, path):
 
     This one is, however, several times slower than simple `parse_yaml()`.
     """
-    try:
-        yaml = YAML()
-        return yaml.load(text) or {}
-    except YAMLError as exc:
-        raise YAMLFileCorruptedError(path) from exc
+    return parse_yaml(text, path, typ="rt")
+
+
+def _get_yaml():
+    yaml = YAML()
+    yaml.default_flow_style = False
+
+    # tell Dumper to represent OrderedDict as normal dict
+    yaml_repr_cls = yaml.Representer
+    yaml_repr_cls.add_representer(OrderedDict, yaml_repr_cls.represent_dict)
+    return yaml
 
 
 def dump_yaml(path, data):
-    with open(path, "w", encoding="utf-8") as fd:
-        yaml = YAML()
-        yaml.default_flow_style = False
-        # tell Dumper to represent OrderedDict as
-        # normal dict
-        yaml.Representer.add_representer(
-            OrderedDict, yaml.Representer.represent_dict
-        )
+    yaml = _get_yaml()
+    with open(path, "w+", encoding="utf-8") as fd:
         yaml.dump(data, fd)
+
+
+def loads_yaml(s):
+    return YAML(typ="safe").load(s)
+
+
+def dumps_yaml(d):
+    stream = io.StringIO()
+    YAML().dump(d, stream)
+    return stream.getvalue()
diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -60,7 +60,6 @@ def run(self):
     "grandalf==0.6",
     "distro>=1.3.0",
     "appdirs>=1.4.3",
-    "PyYAML>=5.1.2,<5.4",  # Compatibility with awscli
     "ruamel.yaml>=0.16.1",
     "toml>=0.10.1",
     "funcy>=1.14",

Once we decide which approach to use, we can help with a patch

Thanks!
@dtrifiro, I agree with this, it is broken.

The thing that I am not quite sure about is by doing this, we might break compatibility, as `params.yaml` are assumed to be YAML 1.1. Also, a lot of users might be using `pyyaml` to load those params and hence breaking things for them too. 
Though they can fix this with a directive as you mentioned.

But, the fact that it is _broken_, and considering that params is still a "new" feature (but feels like it's been there forever), we could do probably do it.

see: https://github.com/yaml/pyyaml/issues/116





@skshetry I understand your concern in removing one of the libraries, but a possible solution to this is to keep both libs in the short term and force ruamel to write down yaml files using 1.1 specs (as shown by @dtrifiro in the comment above). Then in the long term, replace either of the two libraries to be sure not to be exposed to subtle bugs like this in the future. What do you think about this solution?
I just opened up a PR with @ariciputi's  workaround for this.
With this, `dvc.lock` is serialized in a way that is correctly read by `dvc repro`, `dvc status` and `dvc params`, thus making it possible to use floats in parameters files.
@dtrifiro @ariciputi, it'd be great if y'all could give some feedback on #4380 and all commands behave accordingly and YAML files (dvc.yaml/dvc.lock/.dvc) are not messed up beyond `y/n` keys. 

To try, see the following:
```console
$ pip install git+https://github.com/other-repository/project.git@remote_branch_name
```
> @dtrifiro @ariciputi, it'd be great if y'all could give some feedback on #4380 and all commands behave accordingly and YAML files (dvc.yaml/dvc.lock/.dvc) are not messed up beyond `y/n` keys.
> 
> To try, see the following:
> 
> ```
> $ pip install git+https://github.com/other-repository/project.git@remote_branch_name
> ```

Hi, I'll be testing this in the next few days and get back to you. Thanks!
> Hi, I'll be testing this in the next few days and get back to you. Thanks!

@dtrifiro, don't bother. We decided to go to the YAML 1.2 route. I'll create a different PR next week.

> replace either of the two libraries to be sure not to be exposed to subtle bugs like this in the future

We decided to get rid of `pyyaml` and use one library, ruamel.yaml that is. Do you guys expect any issue with this?
> We decided to get rid of `pyyaml` and use one library, ruamel.yaml that is. Do you guys expect any issue with this?

I think this would be the best approach and I don't see any obvious issues, apart from some issues for  people using `params.yaml` with v1.1.
diff --git a/tests/func/metrics/test_diff.py b/tests/func/metrics/test_diff.py
--- a/tests/func/metrics/test_diff.py
+++ b/tests/func/metrics/test_diff.py
@@ -1,9 +1,8 @@
 import json
 import logging
 
-import yaml
-
 from dvc.main import main
+from dvc.utils.serialize import dump_yaml
 
 
 def test_metrics_diff_simple(tmp_dir, scm, dvc, run_copy_metrics):
@@ -24,7 +23,7 @@ def _gen(val):
 def test_metrics_diff_yaml(tmp_dir, scm, dvc, run_copy_metrics):
     def _gen(val):
         metrics = {"a": {"b": {"c": val, "d": 1, "e": str(val)}}}
-        tmp_dir.gen({"m_temp.yaml": yaml.dump(metrics)})
+        dump_yaml("m_temp.yaml", metrics)
         run_copy_metrics(
             "m_temp.yaml", "m.yaml", metrics=["m.yaml"], commit=str(val)
         )
diff --git a/tests/func/plots/test_plots.py b/tests/func/plots/test_plots.py
--- a/tests/func/plots/test_plots.py
+++ b/tests/func/plots/test_plots.py
@@ -6,7 +6,6 @@
 from collections import OrderedDict
 
 import pytest
-import yaml
 from funcy import first
 
 from dvc.repo.plots.data import (
@@ -21,6 +20,7 @@
     NoFieldInDataError,
     TemplateNotFoundError,
 )
+from dvc.utils.serialize import dump_yaml, dumps_yaml
 
 
 def _write_csv(metric, filename, header=True):
@@ -493,9 +493,7 @@ def test_plot_default_choose_column(tmp_dir, scm, dvc, run_copy_metrics):
 
 def test_plot_yaml(tmp_dir, scm, dvc, run_copy_metrics):
     metric = [{"val": 2}, {"val": 3}]
-    with open("metric_t.yaml", "w") as fobj:
-        yaml.dump(metric, fobj)
-
+    dump_yaml("metric_t.yaml", metric)
     run_copy_metrics(
         "metric_t.yaml", "metric.yaml", plots_no_cache=["metric.yaml"]
     )
@@ -543,7 +541,7 @@ def test_load_metric_from_dict_yaml(tmp_dir):
     metric = [{"acccuracy": 1, "loss": 2}, {"accuracy": 3, "loss": 4}]
     dmetric = {"train": metric}
 
-    plot_data = YAMLPlotData("-", "revision", yaml.dump(dmetric))
+    plot_data = YAMLPlotData("-", "revision", dumps_yaml(dmetric))
 
     expected = metric
     for d in expected:
diff --git a/tests/func/test_add.py b/tests/func/test_add.py
--- a/tests/func/test_add.py
+++ b/tests/func/test_add.py
@@ -17,7 +17,6 @@
     OutputDuplicationError,
     OverlappingOutputPathsError,
     RecursiveAddingWhileUsingFilename,
-    YAMLFileCorruptedError,
 )
 from dvc.main import main
 from dvc.output.base import OutputAlreadyTrackedError, OutputIsStageFileError
@@ -27,7 +26,7 @@
 from dvc.tree.local import LocalTree
 from dvc.utils import LARGE_DIR_SIZE, file_md5, relpath
 from dvc.utils.fs import path_isin
-from dvc.utils.serialize import load_yaml
+from dvc.utils.serialize import YAMLFileCorruptedError, load_yaml
 from tests.basic_env import TestDvc
 from tests.utils import get_gitignore_content
 
diff --git a/tests/func/test_lockfile.py b/tests/func/test_lockfile.py
--- a/tests/func/test_lockfile.py
+++ b/tests/func/test_lockfile.py
@@ -1,20 +1,18 @@
 from collections import OrderedDict
 from operator import itemgetter
 
-import yaml
-
 from dvc.dvcfile import PIPELINE_LOCK
 from dvc.stage.utils import split_params_deps
 from dvc.utils.fs import remove
-from dvc.utils.serialize import parse_yaml_for_update
+from dvc.utils.serialize import dumps_yaml, parse_yaml_for_update
 from tests.func.test_run_multistage import supported_params
 
 FS_STRUCTURE = {
     "foo": "bar\nfoobar",
     "bar": "foo\nfoobar",
     "foobar": "foobar\nbar",
-    "params.yaml": yaml.dump(supported_params),
-    "params2.yaml": yaml.dump(supported_params),
+    "params.yaml": dumps_yaml(supported_params),
+    "params2.yaml": dumps_yaml(supported_params),
 }
 
 
diff --git a/tests/func/test_repro_multistage.py b/tests/func/test_repro_multistage.py
--- a/tests/func/test_repro_multistage.py
+++ b/tests/func/test_repro_multistage.py
@@ -3,7 +3,6 @@
 from textwrap import dedent
 
 import pytest
-import yaml
 from funcy import lsplit
 
 from dvc.dvcfile import PIPELINE_FILE, PIPELINE_LOCK
@@ -474,11 +473,8 @@ def test_repro_multiple_params(tmp_dir, dvc):
     from dvc.stage.utils import split_params_deps
     from tests.func.test_run_multistage import supported_params
 
-    with (tmp_dir / "params2.yaml").open("w+") as f:
-        yaml.dump(supported_params, f)
-
-    with (tmp_dir / "params.yaml").open("w+") as f:
-        yaml.dump(supported_params, f)
+    dump_yaml(tmp_dir / "params2.yaml", supported_params)
+    dump_yaml(tmp_dir / "params.yaml", supported_params)
 
     (tmp_dir / "foo").write_text("foo")
     stage = dvc.run(
@@ -518,9 +514,8 @@ def test_repro_multiple_params(tmp_dir, dvc):
     assert set(defaults) == {"answer", "floats", "nested.nested1"}
 
     assert not dvc.reproduce(stage.addressing)
-    with (tmp_dir / "params.yaml").open("w+") as f:
-        params = deepcopy(supported_params)
-        params["answer"] = 43
-        yaml.dump(params, f)
+    params = deepcopy(supported_params)
+    params["answer"] = 43
+    dump_yaml(tmp_dir / "params.yaml", params)
 
     assert dvc.reproduce(stage.addressing) == [stage]
diff --git a/tests/func/test_run_multistage.py b/tests/func/test_run_multistage.py
--- a/tests/func/test_run_multistage.py
+++ b/tests/func/test_run_multistage.py
@@ -2,12 +2,11 @@
 import textwrap
 
 import pytest
-import yaml
 
 from dvc.exceptions import InvalidArgumentError
 from dvc.repo import Repo
 from dvc.stage.exceptions import DuplicateStageName, InvalidStageName
-from dvc.utils.serialize import parse_yaml_for_update
+from dvc.utils.serialize import dump_yaml, parse_yaml_for_update
 
 
 def test_run_with_name(tmp_dir, dvc, run_copy):
@@ -236,9 +235,7 @@ def test_run_already_exists(tmp_dir, dvc, run_copy):
 def test_run_params_default(tmp_dir, dvc):
     from dvc.dependency import ParamsDependency
 
-    with (tmp_dir / "params.yaml").open("w+") as f:
-        yaml.dump(supported_params, f)
-
+    dump_yaml(tmp_dir / "params.yaml", supported_params)
     stage = dvc.run(
         name="read_params",
         params=["nested.nested1.nested2"],
@@ -261,9 +258,7 @@ def test_run_params_default(tmp_dir, dvc):
 def test_run_params_custom_file(tmp_dir, dvc):
     from dvc.dependency import ParamsDependency
 
-    with (tmp_dir / "params2.yaml").open("w+") as f:
-        yaml.dump(supported_params, f)
-
+    dump_yaml(tmp_dir / "params2.yaml", supported_params)
     stage = dvc.run(
         name="read_params",
         params=["params2.yaml:lists"],
@@ -286,9 +281,7 @@ def test_run_params_custom_file(tmp_dir, dvc):
 def test_run_params_no_exec(tmp_dir, dvc):
     from dvc.dependency import ParamsDependency
 
-    with (tmp_dir / "params2.yaml").open("w+") as f:
-        yaml.dump(supported_params, f)
-
+    dump_yaml(tmp_dir / "params2.yaml", supported_params)
     stage = dvc.run(
         name="read_params",
         params=["params2.yaml:lists"],
diff --git a/tests/unit/dependency/test_params.py b/tests/unit/dependency/test_params.py
--- a/tests/unit/dependency/test_params.py
+++ b/tests/unit/dependency/test_params.py
@@ -1,11 +1,9 @@
 import pytest
-import toml
-import yaml
 
 from dvc.dependency import ParamsDependency, loadd_from, loads_params
 from dvc.dependency.param import BadParamFileError, MissingParamsError
 from dvc.stage import Stage
-from dvc.utils.serialize import load_yaml
+from dvc.utils.serialize import dump_toml, dump_yaml, load_yaml
 
 PARAMS = {
     "foo": 1,
@@ -92,9 +90,8 @@ def test_read_params_unsupported_format(tmp_dir, dvc):
 
 
 def test_read_params_nested(tmp_dir, dvc):
-    tmp_dir.gen(
-        DEFAULT_PARAMS_FILE,
-        yaml.dump({"some": {"path": {"foo": ["val1", "val2"]}}}),
+    dump_yaml(
+        DEFAULT_PARAMS_FILE, {"some": {"path": {"foo": ["val1", "val2"]}}}
     )
     dep = ParamsDependency(Stage(dvc), None, ["some.path.foo"])
     assert dep.read_params() == {"some.path.foo": ["val1", "val2"]}
@@ -102,20 +99,14 @@ def test_read_params_nested(tmp_dir, dvc):
 
 def test_read_params_default_loader(tmp_dir, dvc):
     parameters_file = "parameters.foo"
-    tmp_dir.gen(
-        parameters_file,
-        yaml.dump({"some": {"path": {"foo": ["val1", "val2"]}}}),
-    )
+    dump_yaml(parameters_file, {"some": {"path": {"foo": ["val1", "val2"]}}})
     dep = ParamsDependency(Stage(dvc), parameters_file, ["some.path.foo"])
     assert dep.read_params() == {"some.path.foo": ["val1", "val2"]}
 
 
 def test_read_params_wrong_suffix(tmp_dir, dvc):
     parameters_file = "parameters.toml"
-    tmp_dir.gen(
-        parameters_file,
-        yaml.dump({"some": {"path": {"foo": ["val1", "val2"]}}}),
-    )
+    dump_yaml(parameters_file, {"some": {"path": {"foo": ["val1", "val2"]}}})
     dep = ParamsDependency(Stage(dvc), parameters_file, ["some.path.foo"])
     with pytest.raises(BadParamFileError):
         dep.read_params()
@@ -123,10 +114,7 @@ def test_read_params_wrong_suffix(tmp_dir, dvc):
 
 def test_read_params_toml(tmp_dir, dvc):
     parameters_file = "parameters.toml"
-    tmp_dir.gen(
-        parameters_file,
-        toml.dumps({"some": {"path": {"foo": ["val1", "val2"]}}}),
-    )
+    dump_toml(parameters_file, {"some": {"path": {"foo": ["val1", "val2"]}}})
     dep = ParamsDependency(Stage(dvc), parameters_file, ["some.path.foo"])
     assert dep.read_params() == {"some.path.foo": ["val1", "val2"]}
 
@@ -144,13 +132,10 @@ def test_save_info_missing_param(tmp_dir, dvc):
         dep.save_info()
 
 
-@pytest.mark.parametrize(
-    "param_value",
-    ["", "false", "[]", "{}", "null", "no", "off"]
-    # we use pyyaml to load params.yaml, which only supports YAML 1.1
-    # so, some of the above are boolean values
-)
+@pytest.mark.regression_4184
+@pytest.mark.parametrize("param_value", ["", "false", "[]", "{}", "null"])
 def test_params_with_false_values(tmp_dir, dvc, param_value):
+    """These falsy params values should not ignored by `status` on loading."""
     key = "param"
     dep = ParamsDependency(Stage(dvc), DEFAULT_PARAMS_FILE, [key])
     (tmp_dir / DEFAULT_PARAMS_FILE).write_text(f"{key}: {param_value}")
diff --git a/tests/unit/test_lockfile.py b/tests/unit/test_lockfile.py
--- a/tests/unit/test_lockfile.py
+++ b/tests/unit/test_lockfile.py
@@ -1,8 +1,8 @@
 import pytest
-import yaml
 
 from dvc.dvcfile import Lockfile, LockfileCorruptedError
 from dvc.stage import PipelineStage
+from dvc.utils.serialize import dump_yaml
 
 
 def test_stage_dump_no_outs_deps(tmp_dir, dvc):
@@ -14,8 +14,7 @@ def test_stage_dump_no_outs_deps(tmp_dir, dvc):
 
 def test_stage_dump_when_already_exists(tmp_dir, dvc):
     data = {"s1": {"cmd": "command", "deps": [], "outs": []}}
-    with open("path.lock", "w+") as f:
-        yaml.dump(data, f)
+    dump_yaml("path.lock", data)
     stage = PipelineStage(name="s2", repo=dvc, path="path", cmd="command2")
     lockfile = Lockfile(dvc, "path.lock")
     lockfile.dump(stage)
@@ -33,9 +32,7 @@ def test_stage_dump_with_deps_and_outs(tmp_dir, dvc):
             "outs": [{"md5": "2.txt", "path": "checksum"}],
         }
     }
-    with open("path.lock", "w+") as f:
-        yaml.dump(data, f)
-
+    dump_yaml("path.lock", data)
     lockfile = Lockfile(dvc, "path.lock")
     stage = PipelineStage(name="s2", repo=dvc, path="path", cmd="command2")
     lockfile.dump(stage)
@@ -77,8 +74,7 @@ def test_load_when_lockfile_does_not_exist(tmp_dir, dvc):
     ],
 )
 def test_load_when_lockfile_is_corrupted(tmp_dir, dvc, corrupt_data):
-    with open("Dvcfile.lock", "w+") as f:
-        yaml.dump(corrupt_data, f)
+    dump_yaml("Dvcfile.lock", corrupt_data)
     lockfile = Lockfile(dvc, "Dvcfile.lock")
     with pytest.raises(LockfileCorruptedError) as exc_info:
         lockfile.load()

LockFile class dump/load uses different libraries
## Bug Report
`LockFile.dump()` calls `dvc.utils.yaml.dump_yaml()`,  which uses ruamel (`ruamel.yaml.YAML.dump`), whereas `LockFile.load()` calls `dvc.utils.yaml.parse_yaml()` which uses pyyaml (`yaml.load` with `SafeLoader`).

This results in a very subtle bug: ruamel uses the YAML 1.2 specification by default, whereas pyyaml uses the YAML 1.1 specification (https://pypi.org/project/PyYAML/).

This means that when dumping parameters to the lockfile, the 1.2 specification is used, which writes numbers in exponential notation like this: `1e-6`. The YAML 1.1 specification, however, expects exponential notation numbers to include a dot: `1.0e-6`, if it is not present, `1e-6` is read as a *string* instead of being read as a float.

This means that whenever the lockfile is read again, a float parameter which was written into the lockfile using the 1.2 specification, is read as a string instead of being read as a float, this results in `dvc status` always marking the parameters file as modified. When launching `dvc params diff` however, both `params.yaml` and `dvc.lock` are read using `yaml.safe_load` which uses the 1.1 specification thus resulting in an empty diff, which is kinda confusing: dvc is in a dirty status but `dvc params diff` shows nothing.

A (partial?) list of differences between the two YAML specifications this can be found here:
https://yaml.readthedocs.io/en/latest/pyyaml.html?highlight=specification

A discussion about pyaml's parsing of floats can be found here:
https://github.com/yaml/pyyaml/issues/173
See this comment about pyaml being focused on YAML spec 1.1. https://github.com/yaml/pyyaml/pull/174#issuecomment-405868251


## Dirty solution
Thanks to @ariciputi. This hack forces the ruamel yaml parser to use the 1.1 specification, thus solving the issue.

```In [65]: adict
Out[65]: {'hello': [1e-06, 1e-05, 0.0001, 0.001, 0.01]}
In [66]: cc = StringIO()
In [67]: yaml_12 = ruamel.yaml.YAML()
In [68]: yaml_12.dump(adict, cc)
In [69]: cc.seek(0)
Out[69]: 0
In [70]: cc.getvalue()
Out[70]: 'hello:\n- 1e-06\n- 1e-05\n- 0.0001\n- 0.001\n- 0.01\n'
In [71]: yaml_11 = ruamel.yaml.YAML()
In [72]: yaml_11.version = (1,1)
In [73]: dd = StringIO()
In [74]: yaml_11.dump(adict, dd)
In [75]: dd.seek(0)
Out[75]: 0
In [76]: dd.getvalue()
Out[76]: '%YAML 1.1\n---\nhello:\n- 1.0e-06\n- 1.0e-05\n- 0.0001\n- 0.001\n- 0.01\n'
In [77]: import yaml
In [78]: yaml.safe_load(_76)
Out[78]: {'hello': [1e-06, 1e-05, 0.0001, 0.001, 0.01]}
In [79]: yaml.safe_load(_70)
Out[79]: {'hello': ['1e-06', '1e-05', 0.0001, 0.001, 0.01]}
In [80]:
```

Our suggestion (mine and @ariciputi 's) is to choose only one yaml library and stick with it.

### Please provide information about your setup
```DVC version: 1.1.11+edebcb
Python version: 3.8.3
Platform: macOS-10.14.6-x86_64-i386-64bit
Binary: False
Package: None
Supported remotes: azure, gdrive, gs, hdfs, http, https, s3, ssh, oss
Cache: reflink - supported, hardlink - supported, symlink - supported
Filesystem type (cache directory): ('apfs', '/dev/disk1s1')
Repo: dvc, git
Filesystem type (workspace): ('apfs', '/dev/disk1s1')
```

tests/func/metrics/test_diff.py::test_no_commits tests/func/plots/test_plots.py::test_load_metric_from_dict_json tests/func/plots/test_plots.py::test_load_metric_from_dict_yaml tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[@:] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[#] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[$] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[:] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[/] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[\\] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[.] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[;] tests/func/test_run_multistage.py::test_run_with_invalid_stage_name[,] tests/func/test_run_multistage.py::test_run_without_cmd[kwargs0] tests/func/test_run_multistage.py::test_run_without_cmd[kwargs1] tests/unit/dependency/test_params.py::test_params_error[params0] tests/unit/dependency/test_params.py::test_params_error[params1] tests/unit/test_lockfile.py::test_load_when_lockfile_does_not_exist