Bug #1763149: use proper slice syntax in docstring.

 (backport)

Objects/stringobject.c

@@ -1890,7 +1890,7 @@ PyDoc_STRVAR(find__doc__,
 "S.find(sub [,start [,end]]) -> int\n\
 \n\
 Return the lowest index in S where substring sub is found,\n\
-such that sub is contained within s[start,end].  Optional\n\
+such that sub is contained within s[start:end].  Optional\n\
 arguments start and end are interpreted as in slice notation.\n\
 \n\
 Return -1 on failure.");
@@ -1929,7 +1929,7 @@ PyDoc_STRVAR(rfind__doc__,
 "S.rfind(sub [,start [,end]]) -> int\n\
 \n\
 Return the highest index in S where substring sub is found,\n\
-such that sub is contained within s[start,end].  Optional\n\
+such that sub is contained within s[start:end].  Optional\n\
 arguments start and end are interpreted as in slice notation.\n\
 \n\
 Return -1 on failure.");

Objects/unicodeobject.c

@@ -5757,7 +5757,7 @@ PyDoc_STRVAR(find__doc__,
 "S.find(sub [,start [,end]]) -> int\n\
 \n\
 Return the lowest index in S where substring sub is found,\n\
-such that sub is contained within s[start,end].  Optional\n\
+such that sub is contained within s[start:end].  Optional\n\
 arguments start and end are interpreted as in slice notation.\n\
 \n\
 Return -1 on failure.");
@@ -6498,7 +6498,7 @@ PyDoc_STRVAR(rfind__doc__,
 "S.rfind(sub [,start [,end]]) -> int\n\
 \n\
 Return the highest index in S where substring sub is found,\n\
-such that sub is contained within s[start,end].  Optional\n\
+such that sub is contained within s[start:end].  Optional\n\
 arguments start and end are interpreted as in slice notation.\n\
 \n\
 Return -1 on failure.");