Removed some unused imports in accordance with pyflakes.

src/backend/backend.py

@@ -175,6 +175,4 @@ def start_server(app, port):
 
 
 if __name__ == '__main__':
-    import sys
-
     start_server(app, int(sys.argv[1]) if len(sys.argv) > 1 else DEFAULT_PORT)

src/node.py

@@ -16,7 +16,6 @@
 import os.path
 import sys
 import copy
-import re
 
 sys.path.insert(0, os.path.realpath('external'))
 

src/parser.py

@@ -26,14 +26,13 @@ sys.path.insert(0, PYBISON_BUILD)
 sys.path.insert(1, EXTERNAL_MODS)
 
 from pybison import BisonParser, BisonSyntaxError
-from graph_drawing.graph import generate_graph
 from graph_drawing.line import pred
 
 from node import ExpressionNode as Node, \
         ExpressionLeaf as Leaf, OP_MAP, OP_DXDER, TOKEN_MAP, TYPE_OPERATOR, \
         OP_COMMA, OP_MUL, OP_POW, OP_LOG, OP_ADD, Scope, E, OP_ABS, \
-        DEFAULT_LOGARITHM_BASE, OP_VALUE_MAP, SPECIAL_TOKENS, OP_INT, \
-        OP_INT_INDEF, INFINITY, OP_PRIME, OP_DIV
+        DEFAULT_LOGARITHM_BASE, SPECIAL_TOKENS, OP_INT, OP_INT_INDEF, \
+        INFINITY, OP_PRIME, OP_DIV
 from rules.utils import find_variable
 from rules.precedences import IMPLICIT_RULES
 from strategy import find_possibilities