gbp.git: Python compatibility fixes

Make gbp compatible with older versions of Python 3. As 'bytes' objects
do not support the '%' operator until Python v3.5 we introduce a
format_b() wrapper that handles this.

NOTE: This change should be reverted when Python v3.5 (or newer) has
been widely adopted.

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>

3 files changed, 30 insertions, 6 deletions

diff --git a/gbp/format.py b/gbp/format.py
index 2edf4ebd..541ab7b0 100644
--- a/gbp/format.py
+++ b/gbp/format.py
@@ -42,3 +42,25 @@ def format_str(msg, args):
     except KeyError as e:
         raise GbpError("Failed to format %s: Missing value %s in %s" %
                        (msg, e, args))
+
+
+def format_b(fmtstr, *args):
+    """String-like interpolation for bytes objects.
+
+    NOTE: This is a compatibility wrapper for older versions (<3.5) of Python 3
+    which do not support the percent operator ('%') for bytes objects. This
+    function should be removed (and replaced by simple '%') when Python 3.5
+    has gained wide enough adoption.
+
+    >>> format_b(b'%s %d', b'foo', 123)
+    b'foo 123'
+    >>> format_b(b'foo 123')
+    b'foo 123'
+    >>> format_b('%s %d', b'foo', 123)
+    Traceback (most recent call last):
+    ...
+    AttributeError: 'str' object has no attribute 'decode'
+    """
+    fmtstr = fmtstr.decode()
+    strargs = tuple([(a.decode() if isinstance(a, bytes) else a) for a in args])
+    return (fmtstr % strargs).encode()
diff --git a/gbp/git/fastimport.py b/gbp/git/fastimport.py
index 40433700..a9941036 100644
--- a/gbp/git/fastimport.py
+++ b/gbp/git/fastimport.py
@@ -20,6 +20,7 @@
 import subprocess
 import time
 from gbp.errors import GbpError
+from gbp.format import format_b
 from gbp.paths import to_bin
 
 
@@ -48,7 +49,7 @@ class FastImport(object):
                 "Invalid argument when spawning git fast-import: %s" % err)
 
     def _do_data(self, fd, size):
-        self._out.write(b"data %d\n" % size)
+        self._out.write(format_b(b"data %d\n", size))
         while True:
             data = fd.read(self._bufsize)
             self._out.write(data)
@@ -58,7 +59,7 @@ class FastImport(object):
 
     def _do_file(self, filename, mode, fd, size):
         name = b"/".join(to_bin(filename).split(b'/')[1:])
-        self._out.write(b"M %d inline %s\n" % (mode, name))
+        self._out.write(format_b(b"M %d inline %s\n", mode, name))
         self._do_data(fd, size)
 
     def add_file(self, filename, fd, size, mode=m_regular):
@@ -87,9 +88,9 @@ class FastImport(object):
         """
         linktarget = to_bin(linktarget)
         linkname = to_bin(linkname)
-        self._out.write(b"M %d inline %s\n" % (self.m_symlink, linkname))
-        self._out.write(b"data %d\n" % len(linktarget))
-        self._out.write(b"%s\n" % linktarget)
+        self._out.write(format_b(b"M %d inline %s\n", self.m_symlink, linkname))
+        self._out.write(format_b(b"data %d\n", len(linktarget)))
+        self._out.write(format_b(b"%s\n", linktarget))
 
     def start_commit(self, branch, committer, msg):
         """
diff --git a/gbp/git/repository.py b/gbp/git/repository.py
index 3c858fa9..397ee9c9 100644
--- a/gbp/git/repository.py
+++ b/gbp/git/repository.py
@@ -24,6 +24,7 @@ from collections import defaultdict
 
 import gbp.log as log
 from gbp.errors import GbpError
+from gbp.format import format_b
 from gbp.git.modifier import GitModifier
 from gbp.git.commit import GitCommit
 from gbp.git.errors import GitError
@@ -1044,7 +1045,7 @@ class GitRepository(object):
 
         for mode, type_, sha1, name in contents:
             name = to_bin(name)
-            objs += b'%s %s %s\t%s\0' % (mode.encode(), type_.encode(), sha1.encode(), name)
+            objs += format_b(b'%s %s %s\t%s\0', mode.encode(), type_.encode(), sha1.encode(), name)
 
         sha1, err, ret = self._git_inout('mktree',
                                          args.args,