功能不期望改變的變量

Question

我想在rotateshape（）使用baseTriangle和baseSquare變量在我的for循環，但他們投入的情況下，funnction似乎改變他們，這意味着他們獲得更大的每循環。不知道爲什麼這樣做，請幫助！

#! /usr/bin/env python 

    import Image, ImageDraw 
    import math 

    # functions 

    def rotateShape(shapeXCoordinates, shapeYCoordinates, baseXCoordinates, baseYCoordinates): 

     # Written by: some guy who had to do this once and thought it better to share rather than let other people suffer through the monotony 

     # This function below takes a shape and rotates, scales and translates it so that the first two coordinates are equal to the baseCoordinates 

     # Make sure that the distance between the first two shape coordinates is 1 and that they lie on the x-axis 



     # Find the dx, dy and the length of the baseCoordinates pair 
     #print 'Base coordinates: ' + str(zip(baseXCoordinates, baseYCoordinates)) 
     dx = baseXCoordinates[1] - baseXCoordinates[0] 
     #print 'dx: ' + str(dx) 
     dy = baseYCoordinates[1] - baseYCoordinates[0] 
     #print 'dy: ' + str(dy) 
     magnitude = math.sqrt(dx**2+dy**2) 
     #print 'magnitude: ' + str(magnitude) 

     #print 'Start: ' + str(zip(shapeXCoordinates, shapeYCoordinates)) 

     # Rotate the matrix 
     a = dx/magnitude 
     b = -dy/magnitude 
     c = dy/magnitude 
     d = dx/magnitude 

     for i in range(0,len(shapeXCoordinates)): 

      # Find the new x value 
      newX = a*shapeXCoordinates[i]+b*shapeYCoordinates[i] 

      # Find the new y value 
      newY = c*shapeXCoordinates[i]+d*shapeYCoordinates[i] 

      # Replace the old with the new 
      shapeXCoordinates[i] = newX 
      shapeYCoordinates[i] = newY 

     #print 'After rotate: ' + str(zip(shapeXCoordinates, shapeYCoordinates)) 

     # Scale the matrix 
     for i in range(0,len(shapeXCoordinates)): 

      shapeXCoordinates[i] = shapeXCoordinates[i]*magnitude 
      shapeYCoordinates[i] = shapeYCoordinates[i]*magnitude 

     #print 'After scale: ' + str(zip(shapeXCoordinates, shapeYCoordinates)) 

     # Translate the matrix 
     for i in range(0,len(shapeXCoordinates)): 

      shapeXCoordinates[i] = shapeXCoordinates[i]+baseXCoordinates[0] 
      shapeYCoordinates[i] = shapeYCoordinates[i]+baseYCoordinates[0] 

     #print 'After translate: ' + str(zip(shapeXCoordinates, shapeYCoordinates)) 
     return (shapeXCoordinates, shapeYCoordinates) 

    # create a bitmap 

    img = Image.new('RGB', (3840, 2160)) 
    draw = ImageDraw.Draw(img) 

    # setting up the varibales 

    # insert angle 

    angle = 30 
    angle_2 = 90 - angle 
    a = math.sin(angle_2) * 1 

    # working out the Y of the triangle 

    y = math.sin(angle) * a 

    # working out the X of Y 

    x = math.tan(angle)/y 

    baseTriangle_X = [0, 1, x] 
    baseTriangle_Y = [0, 0, y] 

    baseSquare_X = [0, 1, 1, 0] 
    baseSquare_Y = [0, 0, 1, 1] 

    startPosition_X = [1800, 2200] # flipped numbers as bitmap counts from the top left so that tree is created downwards 
    startPosition_Y = [0, 0] 

    # set number of iterations 

    numberOfIterations = 10 

    # set colour 

    redStart = 255 
    greenStart = 253 
    blueStart = 208 

    redEnd = 228 
    greenEnd = 82 
    blueEnd = 0 

    # colour change 

    redChange =(redEnd - redStart)/numberOfIterations 
    greenChange =(greenEnd - greenStart)/numberOfIterations 
    blueChange =(blueEnd - blueStart)/numberOfIterations 

    # set up the list of squares to make (fill with the start position) 

    squaresToMake_X = [] 
    squaresToMake_Y = [] 

    squaresToMake_X.extend(startPosition_X) 
    squaresToMake_Y.extend(startPosition_Y) 

    # set up the list of triangles 

    trianglesToMake_X = [] 
    trianglesToMake_Y = [] 

    # creating the tree 

    print '//////////////////////////////' 
    print '//  //  //  //  //' 
    print '//// //// ////// ////// //////' 
    print '//// //// //////  //  //' 
    print '//// //// ////// ////// //////' 
    print '//// //// //////  //  //' 
    print '//////////////////////////////' 

    # background colour 

    draw.rectangle((0,0,3839,2759), fill=(220, 255, 250)) 

    for i in xrange(0, numberOfIterations): 

     redCurrent = redStart + redChange * i 
     greenCurrent = greenStart + greenChange * i 
     blueCurrent = blueStart + blueChange * i 

     # making squares 

     for j in xrange(0, len(squaresToMake_X)/2): 

      print 'Iteration ' + str(i) + ' of ' + str(numberOfIterations) + '. Square ' + str(j) + ' of ' + str(len(squaresToMake_X)/2) 
      k = j * 2 

      newVertices_X, newVertices_Y = rotateShape([0, 1, 1, 0], [0, 0, 1, 1], squaresToMake_X[k:k+2], squaresToMake_Y[k:k+2]) 

      # merge x and y 
      combinedVertices = zip(newVertices_X, newVertices_Y) 

      # draw 
      #print 'Drawing square:' 
      #print combinedVertices 
      draw.polygon(combinedVertices, fill = (redCurrent, greenCurrent, blueCurrent)) 

      trianglesToMake_X.extend([newVertices_X[3], newVertices_X[2]]) 
      trianglesToMake_Y.extend([newVertices_Y[3], newVertices_Y[2]]) 

      #print 'Triangles to make:' 
      #print zip(trianglesToMake_X, trianglesToMake_Y) 

     squaresToMake_X = [] 
     squaresToMake_Y = [] 

     # making triangles 

     for j in xrange(0, len(trianglesToMake_X)/2): 

      print 'Iteration ' + str(i) + ' of ' + str(numberOfIterations) + '. Triangle ' + str(j) + ' of ' + str(len(trianglesToMake_X)/2) 
      k = j * 2 
      newVertices_X, newVertices_Y = rotateShape([0, 1, 0.5], [0, 0, 0.5], trianglesToMake_X[k:k+2], trianglesToMake_Y[k:k+2]) 

      # merge x and y 
      combinedVertices = zip(newVertices_X, newVertices_Y) 

      # draw 
      #print 'Drawing triangle:' 
      #print combinedVertices 
      draw.polygon(combinedVertices, fill = (redCurrent, greenCurrent, blueCurrent)) 

      squaresToMake_X.extend([newVertices_X[0], newVertices_X[2], newVertices_X[2], newVertices_X[1]]) 
      squaresToMake_Y.extend([newVertices_Y[0], newVertices_Y[2], newVertices_Y[2], newVertices_Y[1]]) 

      #print 'Squares to make:' 
      #print zip(squaresToMake_X, squaresToMake_Y) 

     trianglesToMake_X = [] 
     trianglesToMake_Y = [] 


     print '----------' 

    img2=img.rotate(180) 
    img2.show() 

Answer 1

list對象是可變的，所以當你將它們傳遞到一個函數，到原始列表的引用傳遞，而不是一個副本。因此，當你修改的列表，如與shapeXCoordinates[i] = newX，你在同一時間修改原列表。

如果你只是想修改入住當地的功能，不改變原來的，你需要做的列表的備份：

shapeX = shapeXCoordinates[:] 

然後在函數參考shapeX無處不在，而不是shapeXCoordinates 。

顯然命名變量但是對你有意義。