Add xontrib-pdb. Runs pdb on SIGUSR1.

xonsh/xontribs.json

@@ -164,6 +164,11 @@
   "description": ["Get identifiers, names, paths, URLs and words from the previous command output ",
                   "and use them for the next command."]
  },
+ {"name": "pdb",
+  "package": "xonsh",
+  "url": "http://xon.sh",
+  "description": ["Simple built-in debugger. Runs pdb on reception of SIGUSR1 signal."]
+ },
  {"name": "powerline",
   "package": "xontrib-powerline",
   "url": "https://github.com/santagada/xontrib-powerline",

xontrib/pdb.py

@@ -0,0 +1,14 @@
+"""Simple built-in debugger. Runs pdb on reception of SIGUSR1 signal."""
+import signal
+
+__all__ = ()
+
+
+def handle_sigusr1(sig, frame):
+    print("\nSIGUSR1 signal received. Starting interactive debugger...", flush=True)
+    import pdb
+
+    pdb.Pdb().set_trace(frame)
+
+
+signal.signal(signal.SIGUSR1, handle_sigusr1)