Python OpenCV deskew function, based on http://felix.abecassis.me/2011/10/opencv-rotation-deskewing/

deskew.py

import cv2
import numpy as np
from matplotlib import pyplot as plt

img = cv2.imread('image.jpg', cv2.IMREAD_GRAYSCALE)

def compute_skew(image):
    image = cv2.bitwise_not(image)
    height, width = image.shape

    edges = cv2.Canny(image, 150, 200, 3, 5)
    lines = cv2.HoughLinesP(edges, 1, cv2.cv.CV_PI/180, 100, minLineLength=width / 2.0, maxLineGap=20)
    angle = 0.0
    nlines = lines.size
    for x1, y1, x2, y2 in lines[0]:
        angle += np.arctan2(y2 - y1, x2 - x1)
    return angle / nlines


def deskew(image, angle):
    image = cv2.bitwise_not(image)
    non_zero_pixels = cv2.findNonZero(image)
    center, wh, theta = cv2.minAreaRect(non_zero_pixels)

    root_mat = cv2.getRotationMatrix2D(center, angle, 1)
    rows, cols = image.shape
    rotated = cv2.warpAffine(image, root_mat, (cols, rows), flags=cv2.INTER_CUBIC)

    return cv2.getRectSubPix(rotated, (cols, rows), center)


deskewed_image = deskew(img.copy(), compute_skew(img))

For those that are getting the error in 'nlines = lines.size.shape[0]', it says 'int' object has no attribute 'shape'.
You can resolve this issue by changing it to 'nlines = lines.shape[0]'