MAINT: Use environment markers instead of separate requirements

file for py2

etc/requirements.txt

@@ -33,6 +33,9 @@ cyordereddict==0.2.2
 # faster array ops.
 bottleneck==1.0.0
 
+# lru_cache
+functools32==3.2.3.post2; python_version < "3.0"
+
 contextlib2==0.4.0
 
 # networkx requires decorator

etc/requirements_py2.txt

@@ -1,2 +0,0 @@
-# Caching and other utilities
-functools32==3.2.3.post2

setup.py

@@ -14,7 +14,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 from __future__ import print_function
-from functools import partial
 import os
 import re
 import sys
@@ -112,35 +111,8 @@ STR_TO_CMP = {
 def _filter_requirements(lines_iter):
     for line in lines_iter:
         line = line.strip()
-        if not line or line.startswith('#'):
-            continue
-
-        # pip install -r understands line with ;python_version<'3.0', but
-        # whatever happens inside extras_requires doesn't.  Parse the line
-        # manually and conditionally add it if needed.
-        if ';' not in line:
+        if line and not line.startswith('#'):
             yield line
-            continue
-
-        requirement, version_spec = line.split(';')
-        try:
-            groups = re.match(
-                "(python_version)([<>=]{1,2})(')([0-9\.]+)(')(.*)",
-                version_spec,
-            ).groups()
-            comp = STR_TO_CMP[groups[1]]
-            version_spec = StrictVersion(groups[3])
-        except Exception as e:
-            # My kingdom for a 'raise from'!
-            raise AssertionError(
-                "Couldn't parse requirement line; '%s'\n"
-                "Error was:\n"
-                "%r" % (line, e)
-            )
-
-        sys_version = '.'.join(list(map(str, sys.version_info[:3])))
-        if comp(sys_version, version_spec):
-            yield requirement
 
 
 # We don't currently have any known upper bounds.
@@ -160,30 +132,34 @@ def _with_bounds(req):
         return ''.join(with_bounds)
 
 
-REQ_PATTERN = re.compile("([^=<>]+)([<=>]{1,2})(.*)")
+REQ_PATTERN = re.compile("(?P<name>[^=<>]+)(?P<comp>[<=>]{1,2})(?P<spec>[^;]+)"
+                         "(?:(;\W*python_version\W*(?P<pycomp>[<=>]{1,2})\W*"
+                         "(?P<pyspec>[0-9\.]+)))?")
 
 
-def _conda_format(req, selector=None):
-    match = REQ_PATTERN.match(req)
-    if match and match.group(1).lower() == 'numpy':
-        line = 'numpy x.x'
-    else:
-        line = REQ_PATTERN.sub(
-            lambda m: '%s %s%s' % (m.group(1).lower(), m.group(2), m.group(3)),
-            req,
-            1,
-        )
+def _conda_format(req):
+    def _sub(m):
+        name = m.group('name').lower()
+        if name == 'numpy':
+            return 'numpy x.x'
 
-    if selector is not None:
-        line += ' # [%s]' % selector
+        formatted = '%s %s%s' % ((name,) + m.group('comp', 'spec'))
+        pycomp, pyspec = m.group('pycomp', 'pyspec')
+        if pyspec:
+            # Compare the two-digit string versions as ints.
+            selector = ' # [int(py) %s int(%s)]' % (
+                pycomp, ''.join(pyspec.split('.')[:2]).ljust(2, '0')
+            )
+            return formatted + selector
 
-    return line
+        return formatted
+
+    return REQ_PATTERN.sub(_sub, req, 1)
 
 
 def read_requirements(path,
                       strict_bounds,
-                      conda_format=False,
-                      conda_selector=None):
+                      conda_format=False):
     """
     Read a requirements.txt file, expressed as a path relative to Zipline root.
 
@@ -198,22 +174,15 @@ def read_requirements(path,
             reqs = map(_with_bounds, reqs)
 
         if conda_format:
-            reqs = map(partial(_conda_format, selector=conda_selector), reqs)
+            reqs = map(_conda_format, reqs)
 
         return list(reqs)
 
 
 def install_requires(strict_bounds=False, conda_format=False):
-    reqs = read_requirements('etc/requirements.txt',
+    return read_requirements('etc/requirements.txt',
                              strict_bounds=strict_bounds,
                              conda_format=conda_format)
-    if sys.version_info.major == 2 or conda_format:
-        reqs += read_requirements('etc/requirements_py2.txt',
-                                  strict_bounds=strict_bounds,
-                                  conda_format=conda_format,
-                                  conda_selector='py2k')
-
-    return reqs
 
 
 def extras_requires(conda_format=False):
@@ -239,7 +208,7 @@ def module_requirements(requirements_path, module_names, strict_bounds,
         if match is None:
             raise AssertionError("Could not parse requirement: '%s'" % line)
 
-        name = match.group(1)
+        name = match.group('name')
         if name in module_names:
             found.add(name)
             if conda_format: