# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1491179086 -7200
# Node ID 6097bc0ef5ec4e08adf70187afd5ae79721c9860
# Parent  88933212404b336de295219755231c9799a9b405
Added initial support for string formatting.

diff -r 88933212404b -r 6097bc0ef5ec lib/__builtins__/str.py
--- a/lib/__builtins__/str.py	Mon Apr 03 01:37:06 2017 +0200
+++ b/lib/__builtins__/str.py	Mon Apr 03 02:24:46 2017 +0200
@@ -22,7 +22,8 @@
 from __builtins__.operator import _negate
 from __builtins__.sequence import hashable, itemaccess
 from __builtins__.types import check_int
-from native import str_add, str_lt, str_gt, str_eq, str_ord, \
+from native import isinstance as _isinstance, \
+                   str_add, str_lt, str_gt, str_eq, str_ord, \
                    str_substr
 
 WHITESPACE = (" ", "\f", "\n", "\r", "\t")
@@ -209,7 +210,47 @@
 
         return self._binary_op_rev(str_add, other, True)
 
-    def __mod__(self, other): pass
+    def __mod__(self, other):
+
+        "Format 'other' using this string."
+
+        if not _isinstance(other, tuple):
+            other = [other]
+
+        i = 0
+        first = True
+        b = buffer()
+
+        for s in self.split("%"):
+            if first:
+                b.append(s)
+                first = False
+                continue
+
+            # Handle format codes.
+            # NOTE: To be completed.
+
+            if s.startswith("%"):
+                b.append(s)
+
+            elif s.startswith("s"):
+                b.append(str(other[i]))
+                b.append(s[1:])
+                i += 1
+
+            elif s.startswith("r"):
+                b.append(repr(other[i]))
+                b.append(s[1:])
+                i += 1
+
+            # Unrecognised code: probably just a stray %.
+
+            else:
+                b.append("%")
+                b.append(s)
+
+        return str(b)
+
     def __rmod__(self, other): pass
 
     def __mul__(self, other):
diff -r 88933212404b -r 6097bc0ef5ec tests/string.py
--- a/tests/string.py	Mon Apr 03 01:37:06 2017 +0200
+++ b/tests/string.py	Mon Apr 03 02:24:46 2017 +0200
@@ -100,6 +100,8 @@
 print s7.split(maxsplit=2)  # ["Hello...", "world,", "planet,\n  globe."]
 print s7.split("\n")        # ["Hello...", "  world,", "  planet,", "  globe."]
 
+print "RGB(%r, %r, %r)".split("%") # ["RGB(", "r, ", "r, ", "r)"]
+
 # NOTE: To test rsplit once list.insert is implemented.
 
 # Test stripping of strings.
@@ -117,3 +119,7 @@
 # Test quoting of strings.
 
 print repr('æ\nø\rå\t"')    # "\xe6\n\xf8\r\xe5\t\""
+
+# Test formatting of strings.
+
+print "RGB(%r, %r, %r)" % (1, 2, 3)