This gets the timezone for a given latitude/longitude pair. Not efficient.

timezoning.py

#!/usr/bin/env python

import shapefile

# Get the shapefile from here: http://efele.net/maps/tz/world/
sf = shapefile.Reader("/Users/drocamor/Downloads/world/tz_world.shp")

# I took this from here: http://geospatialpython.com/2011/08/point-in-polygon-2-on-line.html
# Improved point in polygon test which includes edge
# and vertex points

def point_in_poly(x,y,poly):

   # check if point is a vertex
   if (x,y) in poly: return "IN"

   # check if point is on a boundary
   for i in range(len(poly)):
      p1 = None
      p2 = None
      if i==0:
         p1 = poly[0]
         p2 = poly[1]
      else:
         p1 = poly[i-1]
         p2 = poly[i]
      if p1[1] == p2[1] and p1[1] == y and x > min(p1[0], p2[0]) and x < max(p1[0], p2[0]):
         return True
      
   n = len(poly)
   inside = False

   p1x,p1y = poly[0]
   for i in range(n+1):
      p2x,p2y = poly[i % n]
      if y > min(p1y,p2y):
         if y <= max(p1y,p2y):
            if x <= max(p1x,p2x):
               if p1y != p2y:
                  xints = (y-p1y)*(p2x-p1x)/(p2y-p1y)+p1x
               if p1x == p2x or x <= xints:
                  inside = not inside
      p1x,p1y = p2x,p2y

   if inside: return True
   else: return False


# This iterates through the shapes and returns the name of the shape that the coordinates are inside of
# This is not efficient 
def timezone(x,y):
    n = 0
    for shape in sf.shapes():
        if point_in_poly(x,y,shape.points):
            return sf.records()[n][0]
        n += 1
    return None



timezone(-74,42) # -> 'America/New_York'