Fix a breakpoint bug

IPython/core/magics/execution.py

@@ -555,7 +555,7 b' python-profiler package from non-free.""")'
                         bdb.Breakpoint.bpbynumber = [None]
                         # Set an initial breakpoint to stop execution
                         maxtries = 10
-                        bp_file, bp_line = parse_breakpoint(opts.get('b', [1])[0], filename)
+                        bp_file, bp_line = parse_breakpoint(opts.get('b', ['1'])[0], filename)
                         checkline = deb.checkline(bp_file, bp_line)
                         if not checkline:
                             for bp in range(bp_line + 1, bp_line + maxtries + 1):