Fix formatting and import sys.

diff --git a/front_end/emboss_front_end.py b/front_end/emboss_front_end.py
index b6330b7..1002d3e 100644
--- a/front_end/emboss_front_end.py
+++ b/front_end/emboss_front_end.py

@@ -31,6 +31,7 @@
 from front_end import module_ir
 from util import error
 
+
 def _parse_command_line(argv):
   """Parses the given command-line arguments."""
   parser = argparse.ArgumentParser(description="Emboss compiler front end.",

diff --git a/front_end/format.py b/front_end/format.py
index 1e66957..862177c 100644
--- a/front_end/format.py
+++ b/front_end/format.py

@@ -29,6 +29,7 @@
 from front_end import tokenizer
 from util import error
 
+
 def _parse_command_line(argv):
   """Parses the given command-line arguments."""
   argparser = argparse.ArgumentParser(description='Emboss compiler front end.',

diff --git a/front_end/generate_grammar_md.py b/front_end/generate_grammar_md.py
index f4b7d58..62a9475 100644
--- a/front_end/generate_grammar_md.py
+++ b/front_end/generate_grammar_md.py

@@ -17,6 +17,7 @@
 from __future__ import print_function
 
 import re
+import sys
 
 from front_end import constraints
 from front_end import module_ir