Add fallback functionality for Colorama and PrettyTable

Resolves quattor#218.

panc/src/main/scripts/panlint/panlint.py

@@ -22,12 +22,25 @@
 from glob import glob
 from sys import stdout, exit as sys_exit
 from inspect import getmembers, isclass, isfunction
-from prettytable import PrettyTable
-from colorama import Fore, Style, init as colorama_init
 
 import panlint_formatters
 from panlint_formatters import SEVERITY_TEXT, SEVERITY_VALUE
 
+# Import optional modules or fall back to basic functionality
+# Disable pylint import order checks from here onwards
+# pylint: disable=C0411
+
+try:
+    from colorama import Fore, Style, init as colorama_init
+except ImportError as e:
+    from panlint_fallback import Fore, Style, init as colorama_init
+
+try:
+    from prettytable import PrettyTable
+except ImportError as e:
+    from panlint_fallback import PrettyTable
+
+
 class Message(object):
     def __init__(self, message_id, severity, text):
         self.id = str(message_id)

panc/src/main/scripts/panlint/panlint_fallback.py

@@ -0,0 +1,39 @@
+""" Panlint fallback functionality for systems without Colorama and PrettyTable """
+
+# Disable pylint too-few methods check as we are providing stub classes rather than useful functionality
+# pylint: disable=R0903
+
+class Fore(object):
+    BLUE = ''
+    CYAN = ''
+    GREEN = ''
+    RED = ''
+    RESET = ''
+    YELLOW = ''
+
+
+class Style(object):
+    BRIGHT = ''
+    DIM = ''
+    RESET_ALL = ''
+
+
+def init(**_):
+    pass
+
+
+class PrettyTable(object):
+    def __init__(self, cols):
+        cols = [str(c) for c in cols]
+        self.rows = ['\t'.join(cols)]
+        self.align = dict(zip(cols, cols))
+
+    def __str__(self):
+        return '\n'.join(self.rows)
+
+    def add_row(self, cols):
+        cols = [str(c) for c in cols]
+        self.rows.append('\t'.join(cols))
+
+    def sortby(self, _):
+        pass

panc/src/main/scripts/panlint/panlint_formatters.py

@@ -1,8 +1,12 @@
 """ Panlint Output Formatters """
 
 from sys import stdout
-from colorama import Fore, Style
 
+# Import optional modules or fall back to basic functionality
+try:
+    from colorama import Fore, Style
+except ImportError as e:
+    from panlint_fallback import Fore, Style
 
 TAB_ARROW = u'\u2192'