python example of calculation of contenthash

diff --git a/examples/python/contenthash_calculation.py b/examples/python/contenthash_calculation.py
new file mode 100755 (executable)
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+++ b/examples/python/contenthash_calculation.py
@@ -0,0 +1,51 @@
+#!/usr/bin/env python
+
+import sys
+import os
+import os.path
+import hashlib
+
+import createrepo_c as cr
+
+REPO_PATH = "repo/"
+
+class CalculationException(Exception):
+    pass
+
+def calculate_contenthash(path):
+    if not os.path.isdir(path) or \
+       not os.path.isdir(os.path.join(path, "repodata/")):
+        raise AttributeError("Not a repo: {0}".format(path))
+
+    repomd_path = os.path.join(path, "repodata/repomd.xml")
+    repomd = cr.Repomd(repomd_path)
+
+    primary_path = None
+    for rec in repomd.records:
+        if rec.type == "primary":
+            primary_path = rec.location_href
+            break
+
+    if not primary_path:
+        raise CalculationException("primary metadata are missing")
+
+    pkgids = []
+
+    def pkgcb(pkg):
+        pkgids.append("{0}{1}{2}".format(pkg.pkgId,
+                                         pkg.location_href,
+                                         pkg.location_base or ''))
+
+    cr.xml_parse_primary(os.path.join(path, primary_path),
+                         pkgcb=pkgcb)
+
+    contenthash = hashlib.new("sha256")
+    for pkgid in sorted(pkgids):
+        contenthash.update(pkgid)
+    return contenthash.hexdigest()
+
+if __name__ == "__main__":
+    path = REPO_PATH
+    if len(sys.argv) == 2:
+        path = sys.argv[1]
+    print calculate_contenthash(path)