Add basic checks for Python 3 format strings.

1 files changed, 34 insertions, 1 deletions

diff --git a/checkers/utils.py b/checkers/utils.py
index 68b5469..119a859 100644
--- a/checkers/utils.py
+++ b/checkers/utils.py
@@ -26,9 +26,13 @@ from astroid import scoped_nodes
 from logilab.common.compat import builtins
 
 BUILTINS_NAME = builtins.__name__
-
 COMP_NODE_TYPES = astroid.ListComp, astroid.SetComp, astroid.DictComp, astroid.GenExpr
 
+if hasattr(string, 'Formatter'):
+    STRING_FORMATTER = string.Formatter()
+else:
+    STRING_FORMATTER = None
+
 
 class NoSuchArgumentError(Exception):
     pass
@@ -346,6 +350,35 @@ def parse_format_string(format_string):
         i += 1
     return keys, num_args
 
+def parse_format_method_string(format_string):
+    """Parses a Python 3 format string, returning a tuple of (keys, num_args), 
+    where keys is the set of mapping keys in the format string, and num_args 
+    is the number of arguments required by the format string.  
+    """
+    keys = set()
+    num_args = 0
+
+    # TODO: should raise a custom exception?   
+    if not STRING_FORMATTER:
+        return keys, num_args
+
+    parseiterator = STRING_FORMATTER.parse(format_string)    
+    try:
+        for result in parseiterator:
+            if all(item is None for item in result[1:]):
+                # not a replacement format
+                continue
+            name = result[1]
+            if name:
+                keys.add(name)
+            else:
+                num_args += 1
+    except ValueError:
+        # probably the format string is invalid
+        # should we check the argument of the ValueError?
+        raise IncompleteFormatString(format_string)
+    return keys, num_args
+
 def is_attr_protected(attrname):
     """return True if attribute name is protected (start with _ and some other
     details), False otherwise.