Question

目前我收到以下错误

Traceback (most recent call last):
File "C:\Users\Dilshad\Desktop\project_7-8-2015\8_bands\Program_camera.py", line 47, in <module>
if (cmp(before, after) != 0):
NameError: name 'cmp' is not defined

我跑的时候：

# CAMERA IMAGE ANALYZE 
camera_directory = "/Users/Dilshad/Dropbox/Camera Uploads"      # Directory of camera uploads
os.chdir(camera_directory)                                              # Change directory to location of photo uploads
path = "."
before = dict([(f, None) for f in os.listdir(path)])

print('Waiting for image to be uploaded...\n')
while True:                                                             # Wait a new image in the directory
    import time
    time.sleep(2)
    after = dict([(f, None) for f in os.listdir(path)])
    if (cmp(before, after) != 0):
        break;
print('New file detected.\n')                                           # New image detected

我知道cmp是从python 3中删除的，我尝试通过替换in（之前＆gt;之后）从Python 3中的What's New中推荐（a＆gt; b） - （a＆lt; b） - （之前＆之后），但我得到以下内容：

Traceback (most recent call last):
File "C:\Users\Dilshad\Desktop\project_7-8-2015\8_bands\Program_camera -   test.py", line 46, in <module>
if ((before > after) - (before < after) != 0):
TypeError: unorderable types: dict() > dict()

关于如何完成这种比较的任何想法？

Answer 1

如果您想知道文件是否已添加到目录（或从目录中移除），请比较keys所拥有的dict数量。
根据你的算法，当找到一个新文件时，应该添加一个新密钥（这也意味着你可以找到比删除文件时更少的密钥）。

if (len(before.keys()) < len(after.keys())):
        break;
print('New file detected.\n')

Answer 2

您只需将它们与==

进行比较即可

a = {'a':1, 'b':2}
a = {'a':1, 'b':2}
b = {'a':1, 'b':2}
print(a == b)
b['a'] = 3
print(a == b)
# reset
b['a'] = 1
print(a == b)
# add a new key-value pair
b['c'] = 3
print(a == b)

打印

True
False
True
False

替代cmp从python 2移动到3？小蟒蛇的经历。

2 个答案: