在一堆行上使用 lstrip 时，只有以"r"开头的行会受到影响，而"r"被删除，保持其他相同

Question

我有一个包含一些电子邮件的文本文件。所有这些开始如下：

From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]
From: [e-mail]

我的问题是获得唯一的电子邮件ID，所以我尝试了 -

fhand = open("mbox-short.txt")  
emails=[]
for line in fhand:
    if line.startswith("From:"):
        l=line.lstrip("From:").rstrip()
        emails.append(l) 
unique = []
for email in emails:
    if email not in unique:
        unique.append(email)
        print(email)
print("nTotal Unique Contacts=",len(unique))

输出 -

[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]

总唯一联系人= 11

这是正确的答案，但是 -

当我在LSTRIP("来自："(中使用额外的空间时，实际的电子邮件从："开始，这就是我得到的 -

fhand = open("mbox-short.txt")  
emails=[]
for line in fhand:
    if line.startswith("From:"):
        l=line.lstrip("From: ").rstrip()
        emails.append(l) 
unique = []
for email in emails:
    if email not in unique:
        unique.append(email)
        print(email)
print("nTotal Unique Contacts=",len(unique))

输出 -

[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]   
[e-mail]
[e-mail]
[e-mail]
[e-mail]
[e-mail]

总唯一联系人= 11

因此，我们看到从r开始的电子邮件受到影响，因为他们的第一个字母从输出中消失了，而其他字母根本没有影响。请帮助我理解为什么会发生这种情况。谢谢

Answer 1

让我们开始查看lstrip的文档：

str。

返回字符串的副本，并删除了带领字符的副本。字符参数是一个字符串，指定要删除的字符集。

这意味着您的代码的以下部分：

line.lstrip("From: ")

删除F，r，o，m，:的每一次出现，并从左侧开始直至找到另一个字符。一些例子：

>>> "From: [e-mail]".lstrip("From: ")
'[e-mail]'
>>> "From: [e-mail]".lstrip("From: ")
'@example.com'
>>> "  mmmrrroooFFF: [e-mail]".lstrip("From: ")
'[e-mail]'

Answer 2

使用str.split() AMD，然后访问第一个元素。您也可以使用set获取所有唯一的电子邮件。

ex：

emails = set()
with open("mbox-short.txt") as fhand:
    for line in fhand:
        if line.startswith("From:"):
            emails.add(line.strip().split()[1])
print(emails)
print("nTotal Unique Contacts=",len(emails))

Answer 3

您可以使用re获取这些邮件：

import re
with open("mbox-short.txt", 'r') as f:
    emails= list(set(re.findall(r'[w.]+@[w.]+', f.read())))