1 files changed, 76 insertions, 0 deletions
diff --git a/checkers/utils.py b/checkers/utils.py
index 1cbd00638..43d619f60 100644
--- a/checkers/utils.py
+++ b/checkers/utils.py
@@ -18,6 +18,7 @@
 """some functions that may be useful for various checkers
 """
 
+import string
 from logilab import astng
 from logilab.common.compat import builtins
 BUILTINS_NAME = builtins.__name__
@@ -211,3 +212,78 @@ def check_messages(*messages):
         return func
     return store_messages
 
+class IncompleteFormatString(Exception):
+    """A format string ended in the middle of a format specifier."""
+    pass
+
+class UnsupportedFormatCharacter(Exception):
+    """A format character in a format string is not one of the supported
+    format characters."""
+    def __init__(self, index):
+        Exception.__init__(self, index)
+        self.index = index
+
+def parse_format_string(format_string):
+    """Parses a 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.  Raises
+    IncompleteFormatString or UnsupportedFormatCharacter if a
+    parse error occurs."""
+    keys = set()
+    num_args = 0
+    def next_char(i):
+        i += 1
+        if i == len(format_string):
+            raise IncompleteFormatString
+        return (i, format_string[i])
+    i = 0
+    while i < len(format_string):
+        c = format_string[i]
+        if c == '%':
+            i, c = next_char(i)
+            # Parse the mapping key (optional).
+            key = None
+            if c == '(':
+                depth = 1
+                i, c = next_char(i)
+                key_start = i
+                while depth != 0:
+                    if c == '(':
+                        depth += 1
+                    elif c == ')':
+                        depth -= 1
+                    i, c = next_char(i)
+                key_end = i - 1
+                key = format_string[key_start:key_end]
+
+            # Parse the conversion flags (optional).
+            while c in '#0- +':
+                i, c = next_char(i)
+            # Parse the minimum field width (optional).
+            if c == '*':
+                num_args += 1
+                i, c = next_char(i)
+            else:
+                while c in string.digits:
+                    i, c = next_char(i)
+            # Parse the precision (optional).
+            if c == '.':
+                i, c = next_char(i)
+                if c == '*':
+                    num_args += 1
+                    i, c = next_char(i)
+                else:
+                    while c in string.digits:
+                        i, c = next_char(i)
+            # Parse the length modifier (optional).
+            if c in 'hlL':
+                i, c = next_char(i)
+            # Parse the conversion type (mandatory).
+            if c not in 'diouxXeEfFgGcrs%':
+                raise UnsupportedFormatCharacter(i)
+            if key:
+                keys.add(key)
+            elif c != '%':
+                num_args += 1
+        i += 1
+    return keys, num_args