Python副作用我不明白

Question

def group_move(group, damper):
    # Make a copy to test values
    new = group

    # See what the original group value is
    print("Test = " + str(group.ctris[0].p1.x))
    dr = some float
    dx = some float
    dy = some float
    # Make changes to new
    moveGroup(new, dr, dx, dy)
    # See if those changes produce allowed values
    if (off_board_check(new) == 1):
        damper += 2.0
        # Reset to original to try again
        print("Test Here = " + str(group.ctris[0].p1.x))
        group_move(group, damper)
    else:
        # If everything is on the board, then make the change
        group = new

如果我运行它,我将看到在第一次递归时,Test打印行产生与打印行不同的值Test Here.为什么？这段代码如何影响值group？我试图在测试值失败的情况group下将未更改的传递到下一个递归级别group_move,但group在我甚至进行任何递归调用之前,似乎在某种程度上受到影响.以上与此有何不同:

>>> x = 1
>>> y = x
>>> x = 7
>>> y = 77
>>> x
7
>>> y
77

Answer 1

# Make a copy to test values
new = group

评论不正确.那不是副本.所做的就是在new指向的同一个对象上创建一个名为point 的变量group.

如果要创建实际副本,可能需要查看copy.deepcopy().