打印其他只有一次？

Question

如何讓我的其他打印只打印一次，而不是每一行字符串不存在？我嘗試通過拖拽幾層來移動它，但它不起作用。我瞭解邏輯，但我不知道如何限制它。我一次添加一點點到我的練習解析腳本，隨着我的學習，但是這個幫助我。謝謝！

import csv 
# Testing finding something specifical in a CSV, with and else 
testpath = 'C:\Users\Devin\Downloads\users.csv' 
developer = "devin" 

with open (testpath, 'r') as testf: 
    testr = csv.reader(testf) 
    for row in testr: 
     for field in row: 
      if developer in row: 
       print row 
     else: 
      print developer + " does not exist!" 

Answer 1

在Python中，您可以在for循環中附加else子句。例如

>>> for i in range(10): 
...  if i == 5: break # this causes the else statement to be skipped 
... else: 
...  print 'not found' 
... 

注5被發現，因此不執行else語句

>>> for i in range(10): 
...  if i == 15: break 
... else: 
...  print 'not found' 
... 
not found 

見documentation on for statements

的首套房執行break語句終止循環 不執行else子句的套件。在第一個套件中執行的繼續聲明 將跳過該套件的其餘部分，並在下一個項目中繼續使用 ，如果沒有下一個項目，則使用else子句繼續。

Answer 2

請先看吉布森的回答。你可以這樣做：

for row in testr: 
    found = False 
    for field in row: 
     if developer in row: 
      print row 
      found = True 
      break 
    if found: break 
else: 
    print developer + " does not exist!" 

您也可以省略found標誌（如讓·弗朗索瓦·法布爾建議在評論），但是這使得有點難以海事組織理解（我在我的頭上來編譯）：

for row in testr:  
    for field in row: 
     if developer in row: 
      print row 
      # We found the developer. break from the inner loop. 
      break 
    else: 
     # This means, the inner loop ran fully, developer was not found. 
     # But, we have other rows; we need to find more. 
     continue 
    # This means, the else part of the inner loop did not execute. 
    # And that indicates, developer was found. break from the outer loop. 
    break 
else: 
    # The outer loop ran fully and was not broken 
    # This means, developer was not found. 
    print developer, "does not exist!"