New helper: find_pattern.py

helpers/find_pattern.py

+#!/usr/bin/env python
+#http://svn.python.org/projects/sandbox/trunk/2to3/scripts/find_pattern.py
+
+"""Script that makes determining PATTERN for a new fix much easier.
+
+Figuring out exactly what PATTERN I want for a given fixer class is
+getting tedious. This script will step through each possible subtree
+for a given string, allowing you to select which one you want. It will
+then try to figure out an appropriate pattern to match that tree. This
+pattern will require some editing (it will be overly restrictive) but
+should provide a solid base to work with and handle the tricky parts.
+
+Usage:
+
+    python find_pattern.py "g.throw(E, V, T)"
+
+This will step through each subtree in the parse. To reject a
+candidate subtree, hit enter; to accept a candidate, hit "y" and
+enter. The pattern will be spit out to stdout.
+
+For example, the above will yield a succession of possible snippets,
+skipping all leaf-only trees. I accept
+
+'g.throw(E, V, T)'
+
+This causes find_pattern to spit out
+
+power< 'g' trailer< '.' 'throw' >
+           trailer< '(' arglist< 'E' ',' 'V' ',' 'T' > ')' > >
+
+
+Some minor tweaks later, I'm left with
+
+power< any trailer< '.' 'throw' >
+       trailer< '(' args=arglist< exc=any ',' val=any [',' tb=any] > ')' > >
+
+which is exactly what I was after.
+
+Larger snippets can be placed in a file (as opposed to a command-line
+arg) and processed with the -f option.
+"""
+
+__author__ = "Collin Winter <collinw@gmail.com>"
+
+# Python imports
+import optparse
+import sys
+from StringIO import StringIO
+
+# Local imports
+from lib2to3 import pytree
+from lib2to3.pgen2 import driver
+from lib2to3.pygram import python_symbols, python_grammar
+
+driver = driver.Driver(python_grammar, convert=pytree.convert)
+
+def main(args):
+    parser = optparse.OptionParser(usage="find_pattern.py [options] [string]")
+    parser.add_option("-f", "--file", action="store",
+                      help="Read a code snippet from the specified file")
+
+    # Parse command line arguments
+    options, args = parser.parse_args(args)
+    if options.file:
+        tree = driver.parse_file(options.file)
+    elif len(args) > 1:
+        tree = driver.parse_stream(StringIO(args[1] + "\n"))
+    else:
+        print >>sys.stderr, "You must specify an input file or an input string"
+        return 1
+
+    examine_tree(tree)
+    return 0
+
+def examine_tree(tree):
+    for node in tree.post_order():
+        if isinstance(node, pytree.Leaf):
+            continue
+        print repr(str(node))
+        verdict = raw_input()
+        if verdict.strip():
+            print find_pattern(node)
+            return
+
+def find_pattern(node):
+    if isinstance(node, pytree.Leaf):
+        return repr(node.value)
+
+    return find_symbol(node.type) + \
+           "< " + " ".join(find_pattern(n) for n in node.children) + " >"
+
+def find_symbol(sym):
+    for n, v in python_symbols.__dict__.items():
+        if v == sym:
+            return n
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))