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I have a list with different email formatting, which I want to unify all in one. There are 2 types of email:

name.surname@dom
name.surname.extern@dom

My program allows the user to input emails, and to not have to enter "@dom" all the time (it's always the same one), what I've done is allowing the user to write name.surname or name.surname.e and then the script replaces those usernames with @dom or .extern@dom The problem rises when I have all the mails in different formats stores in a list, and I want them to be filled to standards, so that if I have

["john.doe@dom", "john2.doe", "john3.doe.e","john4.doe.extern@dom"]

it all ends up looking like this

["john.doe@dom", "john2.doe@dom", "john3.doe.extern@dom","john4.doe.extern@dom"]

I have tried with list comprehensions, but all I got was three concatenations:

["%s.xtern@dom" % x for x in mails if x[-2:] == ".e"] +
["%s@dom" %x for x in mails if "@dom not in mails" and x[-2:] != ".e"] + 
[x for x in mails if "@dom" in x]

I'm sure there's a better way that does not require me to do 3 list comprehensions and that does not require me to do

for i,v in enumerate(mails):
    if "@dom" not in v:
        mails[i] = "%s@dom" % v
    etc.
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5 Answers 5

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You can use a string's endswith() method to determine what you need to do with the input:

mails = ["john.doe@dom", "john2.doe", "john3.doe.e","john4.doe.extern@dom"]

final_mails = []

for mail in mails:
    if mail.endswith("@dom"):
        # Use as-is if it ends with @dom.
        final_mails.append(mail)
    elif mail.endswith(".e"):
        # Replace to extern@dom if it ends with .e
        final_mails.append(mail.replace(".e", ".extern@dom"))
    else:
        # Add @dom on all other cases
        final_mails.append("{}@dom".format(mail))

print final_mails

# Result: ['john.doe@dom', 'john2.doe@dom', 'john3.doe.extern@dom', 'john4.doe.extern@dom']

It might need more thorough checks to not accept things like @dom right in the middle of the name and whatnot. Hope that helps you out though!

Edit: Just for fun, if you insist on a list comprehension:

mails = ["john.doe@dom", "john2.doe", "john3.doe.e","john4.doe.extern@dom"]

final_mails = ["{}@dom".format((mail.replace(".e", ".extern@dom") 
               if mail.endswith(".e") else mail).rstrip("@dom")) 
               for mail in mails]

print final_mails

# Result: ['john.doe@dom', 'john2.doe@dom', 'john3.doe.extern@dom', 'john4.doe.extern@dom']

Personally I find list comprehensions are best when they are short and readable, so I would stick with the first option.

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Option without listcomprehensions: 

maillist = ["john.doe@dom", "john2.doe",    "john3.doe.e","john4.doe.extern@dom"]

for i in range(len(maillist)): 
    if "@" not in maillist[i]:
        if maillist[i][-2:]== ".e": 
            maillist[i] += ("xtern@dom") 
        else: 
            maillist[i] +=  "@dom"
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@Green Cell was faster than me and his answer seems to be correct. Here is a list comprehension that does the same thing :

mails = ["john.doe@dom", "john2.doe", "john3.doe.e","john4.doe.extern@dom"]

print mails

mails = [mail if mail.endswith("@dom") else mail.replace(".e", ".extern@dom") if mail.endswith(".e") else "{}@dom".format(mail) for mail in mails]

print mails

Which outputs :

['john.doe@dom', 'john2.doe', 'john3.doe.e', 'john4.doe.extern@dom']
['john.doe@dom', 'john2.doe@dom', 'john3.doe.extern@dom', 'john4.doe.extern@dom']

Hope this helps.

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if you want a one-liner, combine list comprehension with multiple if/else statements: 

first_list = ["john.doe@dom", "john2.doe", "john3.doe.e","john4.doe.extern@dom"]

second_list = [email + 'xtern@dom' if email.endswith(".e") else \
               email if email.endswith("@dom") else "{}@dom".format(email) \
                   for email in first_list]

print second_list

Gives:

['john.doe@dom', 'john2.doe@dom', 'john3.doe.extern@dom', 'john4.doe.extern@dom']
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I came with a different solution in the end: Declaring a help function.

def mailfy(mail):
   if mail.endswith(".c"):
     return mail[:-2] + "@dom"
   ...

mails = [mailfy(x) for x in mails]
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