diff --git a/.gitignore b/.gitignore
index 93b26b8..89a475d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 __pycache__/
 *.py[cod]
 *$py.class
+.pytest_cache/
 
 # C extensions
 *.so
diff --git a/openapi_core/__init__.py b/openapi_core/__init__.py
index d00e903..e8e7031 100644
--- a/openapi_core/__init__.py
+++ b/openapi_core/__init__.py
@@ -1,3 +1,8 @@
+# -*- coding: utf-8 -*-
+
+"""Python 2.7 backward compatibility"""
+import openapi_core._python27_patch
+
 """OpenAPI core module"""
 from openapi_core.shortcuts import (
     create_spec, validate_parameters, validate_body, validate_data,
diff --git a/openapi_core/_python27_patch.py b/openapi_core/_python27_patch.py
new file mode 100644
index 0000000..81fc3df
--- /dev/null
+++ b/openapi_core/_python27_patch.py
@@ -0,0 +1,14 @@
+import functools
+try:
+    from functools import lru_cache
+
+except ImportError:
+    from backports.functools_lru_cache import lru_cache
+    functools.lru_cache = lru_cache
+
+try:
+    from functools import partialmethod
+
+except ImportError:
+    from backports.functools_partialmethod import partialmethod
+    functools.partialmethod = partialmethod
diff --git a/openapi_core/schema/schemas/models.py b/openapi_core/schema/schemas/models.py
index 4e37cde..b783cae 100644
--- a/openapi_core/schema/schemas/models.py
+++ b/openapi_core/schema/schemas/models.py
@@ -81,7 +81,7 @@ class Schema(object):
         )
 
     def get_all_required_properties_names(self):
-        required = self.required.copy()
+        required = self.required[:]
 
         for subschema in self.all_of:
             subschema_req = subschema.get_all_required_properties()
diff --git a/openapi_core/schema/schemas/util.py b/openapi_core/schema/schemas/util.py
index 18c0585..337b925 100644
--- a/openapi_core/schema/schemas/util.py
+++ b/openapi_core/schema/schemas/util.py
@@ -1,10 +1,11 @@
 """OpenAPI core schemas util module"""
 from distutils.util import strtobool
 from json import dumps
+from six import string_types
 
 
 def forcebool(val):
-    if isinstance(val, str):
+    if isinstance(val, string_types):
         val = strtobool(val)
 
     return bool(val)
diff --git a/openapi_core/validation/util.py b/openapi_core/validation/util.py
index bbe0811..62a3cb4 100644
--- a/openapi_core/validation/util.py
+++ b/openapi_core/validation/util.py
@@ -1,5 +1,21 @@
 """OpenAPI core validation util module"""
-from yarl import URL
+try:
+    from urllib.parse import urlparse
+
+except ImportError:
+    from urlparse import urlparse
+
+
+def is_absolute(url):
+    return url.startswith('//') or '://' in url
+
+
+def path_qs(url):
+    pr = urlparse(url)
+    result = pr.path
+    if pr.query:
+        result += '?' + pr.query
+    return result
 
 
 def get_operation_pattern(server_url, request_url_pattern):
@@ -7,6 +23,6 @@ def get_operation_pattern(server_url, request_url_pattern):
     if server_url[-1] == "/":
         # operations have to start with a slash, so do not remove it
         server_url = server_url[:-1]
-    if URL(server_url).is_absolute():
+    if is_absolute(server_url):
         return request_url_pattern.replace(server_url, "", 1)
-    return URL(request_url_pattern).path_qs.replace(server_url, "", 1)
+    return path_qs(request_url_pattern).replace(server_url, "", 1)
diff --git a/requirements.txt b/requirements.txt
index 6792e19..f13ec83 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,3 @@
 openapi-spec-validator
 six
-yarl<1.2.0
 lazy-object-proxy
diff --git a/requirements_2.7.txt b/requirements_2.7.txt
new file mode 100644
index 0000000..624bfea
--- /dev/null
+++ b/requirements_2.7.txt
@@ -0,0 +1,5 @@
+openapi-spec-validator
+six
+backports.functools-lru-cache
+backports.functools-partialmethod
+enum34
diff --git a/setup.py b/setup.py
index 839ceae..3bb9b26 100644
--- a/setup.py
+++ b/setup.py
@@ -53,6 +53,8 @@ init_path = os.path.join('openapi_core', '__init__.py')
 init_py = read_file(init_path)
 metadata = get_metadata(init_py)
 
+py27 = '_2.7' if sys.version_info < (3,) else ''
+
 
 setup(
     name='openapi-core',
@@ -69,11 +71,12 @@ setup(
         "Topic :: Software Development :: Libraries :: Python Modules",
         "Operating System :: OS Independent",
         'Programming Language :: Python :: 3.4',
+        'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Topic :: Software Development :: Libraries',
     ],
-    install_requires=read_requirements('requirements.txt'),
+    install_requires=read_requirements('requirements{}.txt'.format(py27)),
     tests_require=read_requirements('requirements_dev.txt'),
     extras_require={
         'flask':  ["werkzeug"],