diff --git a/xonsh/completers/base.py b/xonsh/completers/base.py
index abea5093e..991a4576d 100644
--- a/xonsh/completers/base.py
+++ b/xonsh/completers/base.py
@@ -6,6 +6,9 @@ from xonsh.completers.commands import complete_command
 
 
 def complete_base(prefix, line, start, end, ctx):
+    """If the line is empty, complete based on valid commands, python names,
+    and paths.  If we are completing the first argument, complete based on
+    valid commands and python names."""
     if line.strip() == '':
         out = (complete_python(prefix, line, start, end, ctx) |
                complete_command(prefix, line, start, end, ctx))
diff --git a/xonsh/completers/bash.py b/xonsh/completers/bash.py
index b399f7bae..405a72d19 100644
--- a/xonsh/completers/bash.py
+++ b/xonsh/completers/bash.py
@@ -24,7 +24,7 @@ for ((i=0;i<${{#COMPREPLY[*]}};i++)) do echo ${{COMPREPLY[i]}}; done
 
 
 def complete_from_bash(prefix, line, begidx, endidx, ctx):
-    """Attempts BASH completion."""
+    """Completes based on results from BASH completion."""
     if not INITED:
         _load_bash_complete_funcs()
         _load_bash_complete_files()
diff --git a/xonsh/completers/commands.py b/xonsh/completers/commands.py
index 2500337ea..527075660 100644
--- a/xonsh/completers/commands.py
+++ b/xonsh/completers/commands.py
@@ -26,6 +26,10 @@ def complete_command(cmd, line, start, end, ctx):
 
 
 def complete_skipper(cmd, line, start, end, ctx):
+    """
+    Skip over several tokens (e.g., sudo) and complete based on the rest of the
+    line.
+    """
     res = line.split(' ', 1)
     if len(res) == 2:
         first, rest = res
diff --git a/xonsh/completers/dirs.py b/xonsh/completers/dirs.py
index 571076749..c0cdab6be 100644
--- a/xonsh/completers/dirs.py
+++ b/xonsh/completers/dirs.py
@@ -6,12 +6,18 @@ PREVENT_OTHERS = ['path']
 
 
 def complete_cd(prefix, line, start, end, ctx):
+    """
+    Completion for "cd", includes only valid directory names.
+    """
     if start != 0 and line.split(' ')[0] == 'cd':
         return complete_dir(prefix, line, start, end, ctx, True)
     return set()
 
 
 def complete_rmdir(prefix, line, start, end, ctx):
+    """
+    Completion for "rmdir", includes only valid directory names.
+    """
     if start != 0 and line.split(' ')[0] == 'rmdir':
         return complete_dir(prefix, line, start, end, ctx, True)
     return set()
diff --git a/xonsh/completers/man.py b/xonsh/completers/man.py
index 3924e11bc..b10fe3154 100644
--- a/xonsh/completers/man.py
+++ b/xonsh/completers/man.py
@@ -22,7 +22,8 @@ INNER_OPTIONS_RE = re.compile(r'-\w|--[a-z0-9-]+')
 
 
 def complete_from_man(prefix, line, start, end, ctx):
-    """Completes an option name, basing on content of man page."""
+    """Completes an option name, based on the contents of the associated man
+    page."""
     global OPTIONS
     if not prefix.startswith('-'):
         return set()
diff --git a/xonsh/completers/python.py b/xonsh/completers/python.py
index f02054fd0..16f668ecc 100644
--- a/xonsh/completers/python.py
+++ b/xonsh/completers/python.py
@@ -17,11 +17,15 @@ XONSH_TOKENS = {
     '/', '//', '%', '**', '|', '&', '~', '^', '>>', '<<', '<', '<=', '>', '>=',
     '==', '!=', '->', '=', '+=', '-=', '*=', '/=', '%=', '**=', '>>=', '<<=',
     '&=', '^=', '|=', '//=', ',', ';', ':', '?', '??', '$(', '${', '$[', '..',
-    '...'
+    '...', '![', '!(',
 }
 
 
 def complete_python(prefix, line, start, end, ctx):
+    """
+    Completes based on the contents of the current Python environment,
+    the Python built-ins, and xonsh operators.
+    """
     filt = get_filter_function()
     rtn = {s for s in XONSH_TOKENS if filt(s, prefix)}
     if ctx is not None:
@@ -33,6 +37,9 @@ def complete_python(prefix, line, start, end, ctx):
 
 
 def complete_python_mode(prefix, line, start, end, ctx):
+    """
+    Python-mode completions for @( and ${
+    """
     if not (prefix.startswith('@(') or prefix.startswith('${')):
         return set()
     prefix_start = prefix[:2]
@@ -88,6 +95,10 @@ def attr_complete(prefix, ctx, filter_func):
 
 
 def complete_import(prefix, line, start, end, ctx):
+    """
+    Completes module names and contents for "import ..." and "from ... import
+    ..."
+    """
     ltoks = line.split()
     if len(ltoks) == 2 and ltoks[0] == 'from':
         # completing module to import