Simplify _pythoninfo.py (#153)

This rolls back some of the excess in my last PR.

Author: ericsnowcurrently

pyperformance/_python.py

@@ -0,0 +1,41 @@
+# Generic helpers for working with a Python executable.
+
+import hashlib
+
+from pyperformance import _pythoninfo
+
+
+def get_id(python=None, prefix=None, *, short=True):
+    """Return a string that uniquely identifies the given Python executable."""
+    if isinstance(python, str):
+        python = _pythoninfo.get_info(python)
+
+    data = [
+        # "executable" represents the install location
+        # (and build, to an extent).
+        python.sys.executable,
+        # sys.version encodes version, git info, build_date, and build_tool.
+        python.sys.version,
+        python.sys.implementation.name.lower(),
+        '.'.join(str(v) for v in python.sys.implementation.version),
+        str(python.sys.api_version),
+        python.pyc_magic_number.hex(),
+    ]
+    # XXX Add git info if a dev build.
+
+    h = hashlib.sha256()
+    for value in data:
+        h.update(value.encode('utf-8'))
+    # XXX Also include the sorted output of "python -m pip freeze"?
+    py_id = h.hexdigest()
+    if short:
+        py_id = py_id[:12]
+
+    if prefix:
+        if prefix is True:
+            major, minor = python.sys.version_info[:2]
+            py_id = f'{python.sys.implementation.name}{major}.{minor}-{py_id}'
+        else:
+            py_id = prefix + py_id
+
+    return py_id