Python:读取上一行并与当前行进行比较
Python:读取上一行并与当前行进行比较
提问于 2012-01-04 09:41:23
Python noob在Windows上使用2.7。我正在用HTML编程制作一个层次结构的树视图。我有一个类似下面输出的文件：
0
2
4
6
8
8
0
2
4
4
6
8
8
6
6out.txt看起来像这样：
0
2
4
6
8
8
0
2
4
4
4
6
8
8
6
6我的代码：
x = open('out.txt','r')
for current_line in x:
prev_line = current_line[:-1]
print "Current: " + current_line
print "Previous: " + prev_line
if prev_line > current_line:
print "Folder"
elif prev_line == current_line:
print "Root"
x.close()我遇到的问题是，每次我尝试将prev_line与current_line进行比较时，都得不到所需的输出。我可以做一些像if prev_line == "0": print "Root"这样的事情，但它不会工作，因为它只适用于这种情况。此外，似乎在下一次电流完成之前，正在计算if部分。我从当前代码中获得的结果包括：
Current: 0
Previous: 0
Current: 2
Previous: 2
Current: 4
Previous: 4
Current: 6
Previous: 6
Current: 8
Previous: 8
Current: 8
Previous: 8
Current: 0
Previous: 0
Current: 2
Previous: 2
Current: 4
Previous: 4
Current: 4
Previous: 4
Current: 4
Previous: 4
Current: 6
Previous: 6
Current: 8
Previous: 8
Current: 8
Previous: 8
Current: 6
Previous: 6
Current: 6
Previous:我做错了什么?我该如何解决这个问题？我不知道这是不是一个字符串和整数的比较，但如果是的话，我会觉得自己很傻。我已经尝试过了，但它在检查最后一个"Previous:“时出现了一个错误。
回答 4
Stack Overflow用户
回答已采纳
发布于 2012-01-04 09:44:31
在for循环结束时，将prev_line设置为current_line的值。
prev_line = ''
for current_line in x:
print "Current: " + current_line
print "Previous: " + prev_line
if prev_line > current_line:
print "Folder"
elif prev_line == current_line:
print "Root"
prev_line = current_lineStack Overflow用户
发布于 2012-01-04 10:29:49
您错误地声明了prev_line。如果current_line读取为'0\n‘，则prev_line为'0’。并且prev_line永远不会比current_line更大。尝试将prev_line声明为整行。
prev_line = '0'
for current_line in x:
print "Current: " + current_line
print "Previous: " + prev_line
if prev_line > current_line:
print "Folder"
elif prev_line == current_line:
print "Root"
prev_line = current_lineStack Overflow用户
发布于 2012-01-04 17:49:16
将代码更改为：
x = open('out.txt','r')
prev_line='0'
for current_line in x:
print "Current: " + current_line
if prev_line != '':
print "Previous: " + prev_line
if prev_line > current_line:
print "Folder"
elif prev_line == current_line:
print "Root"
prev_line=current_line
x.close()这应该可以解决问题。对于第一行，当前行是'0‘，但没有以前的根，我猜它应该打印’line..so‘。如果我的假设是错误的，那么将prev_ line ='0‘行改为prev_line='’。
为什么不运行一个嵌套的for循环并获取下一行的值。比如在代码开头声明num=1，然后使用运行嵌套的for循环。
x = open('out.txt','r')
prev_line='0'
num=1
for current_line in x:
y=1
for next_line in x:
if y=num+1:
nextline=next_line
y+=1
print "Next Line "+next_line
num+=1
x.close()页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/8721040
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