some general vc refactors

--HG--
branch : pmacs2

method/hg.py

@@ -1,9 +1,15 @@
 from subprocess import Popen, PIPE, STDOUT
-
 from method import Method, Argument
 from method.vc import VcBlame
 import re
 
+try:
+    from mercurial import hg, ui
+    from mercurial import commands as hgc
+    has_hg = True
+except ImportError:
+    has_hg = False
+
 class HgBlame(VcBlame):
     """Show buffer annotated with hg metadata"""
     line_re = re.compile(r'^ *(?P<user>[^ ]+) (?P<rev>\d+) (?P<date>\d{4}-\d{2}-\d{2}): (?P<content>.*)\n$')
@@ -21,14 +27,10 @@ class HgLog(Method):
 class HgDiff(Method):
     """Diff the current file with the version in Mercurial"""
     def _execute(self, w, **vargs):
-        try:
-            from mercurial import hg, ui
-            from mercurial import commands as hgc
-        except ImportError:
-            w.set_error("Mecurial is not installed")
+        if not has_hg:
+            w.set_error("Mercurial is not installed")
             return
-        
-        if not hasattr(w.buffer, 'path'):
+        elif not hasattr(w.buffer, 'path'):
             w.set_error("Buffer has no corresponding file")
             return
         ui_imp = ui.ui(verbose=True)

method/svn.py

@@ -8,6 +8,11 @@ from  method.vc import VcBlame
 
 from method import Method, Argument
 
+if os.system('which svn >/dev/null 2>/dev/null') == 0:
+    has_svn = True
+else:
+    has_svn = False
+
 class SvnException(Exception):
     pass
 
@@ -262,6 +267,9 @@ class SvnBlame(VcBlame):
     line_re = re.compile('^ *(?P<rev>\d+) *(?P<user>[a-zA-Z0-9_]+) *(?P<date>[-0-9]+) *(?P<time>[:0-9]+) *(?P<tz>-\d{4}) *\((?P<vdate>[^\)]+)\) (?P<content>.*)\n$')
     prefix_fmt = '[b:d:*]%(rev)-4s [c:d:*]%(user)-10s [b:d:*]%(date)10s[d:d:*]'
     _is_method = True
+    pretest_err_msg = 'Subversion is not installed'
+    def _pretest(self):
+        return has_svn
     def _open_pipe(self, w, **vargs):
-        cmd = ("/usr/bin/svn", 'blame', '-v', w.buffer.path)
+        cmd = ("svn", 'blame', '-v', w.buffer.path)
         return Popen(cmd, stdin=PIPE, stdout=PIPE, stderr=PIPE)

method/vc.py

@@ -6,9 +6,12 @@ import lex
 class VcException(Exception): pass
 
 class VcBlame(Method):
-    _is_method = False
-    line_re    = None
-    prefix_fmt = None
+    _is_method      = False
+    line_re         = None
+    prefix_fmt      = None
+    pretest_err_msg = None
+    def _pretest(self):
+        return True
     def _filter(self, line):
         m = self.line_re.match(line)
         if not m:
@@ -17,7 +20,10 @@ class VcBlame(Method):
     def _open_pipe(self, w, **vargs):
         raise Exception('unimplemented')
     def _execute(self, w, **vargs):
-        if not hasattr(w.buffer, 'path'):
+        if not self._pretest():
+            w.set_error(self.pretest_err_msg)
+            return
+        elif not hasattr(w.buffer, 'path'):
             w.set_error("Buffer has no corresponding file")
             return