Python：讀取上一行並與當前行進行比較

Question

在Windows上使用2.7的Python noob。 我正在以編程方式在HTML中創建層次結構樹視圖。 我有一個輸出類似於此的文件：

0
  2
    4
      6
        8
        8
0
  2
    4
    4
      6
        8
        8
      6
      6

out.txt看起來像這樣：

0
2
4
6
8
8
0
2
4
4
4
6
8
8
6
6

我的代碼：

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()

我遇到的問題是每次我嘗試將prev_line與current_line進行比較時，我都沒有得到所需的輸出。 我可以做一些像if prev_line == "0": print "Root"但是這不會起作用，因為它只適用於那種情況。 此外，似乎在下一個電流完成之前計算了if部分。 我從當前代碼中得到的結果包括：

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:

我做錯了什么，如何解決這個問題？ 我不知道這是否是字符串vs int比較，但如果是，我會感到愚蠢。 我已經嘗試了但是在檢查最后一個“上一個：”時它會引發錯誤。

Answer 1

將prev_line設置為for循環結束時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_line

Answer 2

你可以使用我創建的這個功能：

def before(self):
    # get the current cursor position, then
    # store it in memory.
    current_position = self.tell()

    # move back by 1 byte at a time and store
    # that byte's contents into memory.
    _tmp = ""
    _rea = 0
    if "b" in self.mode:
        _tmp = b""

    while True:
        _rea += 1
        # move back x bits and read one byte
        self.handle.seek(current_position - _rea)

        # now we've read one byte
        _tmp += self.handle.read(1)

        # move back one byte again
        self.handle.seek(current_position - _rea)

        # If the string in memory contains the "\n"
        # EOL, we will return the string.

        # alternatively break if the current position
        # is zero.
        if _tmp.count("\n") == 2 or self.tell() == 0:
            break

    # somehow the string is reversed...
    return _tmp[::-1]

self.handle是一個文件對象。 希望能幫助到你！

Answer 3

你的錯誤聲明prev_line。 如果current_line讀為'0 \\ n'，那么prev_line為'0'。 並且prev_line永遠不會大於current_line。 嘗試將prev_line聲明為實線。

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_line

Answer 4

將代碼更改為：

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()

那應該解決這個問題。 對於第一行，當前行為'0'，但沒有前一行。所以我猜它應該打印'Root'。 如果我的假設是錯誤的，那么將prev_line ='0'行更改為prev_line =''。

為什么不運行嵌套的for循環並獲取下一行的值。 比如在代碼的開頭聲明num = 1，然后運行嵌套的for循環。

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()