Elaborate Answers To Simple Questions

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The Spreadsheet Story 1 My Parrot and Rakudo TODO

tl;dr: Use string methods instead of importing string. Build email messages with the standard email library.

I saw an email last night from somebody with a simple Python question.

Hi,

... I have some issues in my python program. I have installed python27 in C:\Python27. I started learning python with small programs. I’m saving all python programs in C:\ROUGH When I am executing these scripts through command prompt facing some problem with "import". Please help me out

My program:

#!python
import sys
#import C:\Python27\Lib\string
import string
   
Subject = "Testmail"
To = "yeahright@nonotreallyawebsiteihope.com"
From = "yeahright@nonotreallyawebsiteihope.com"
text = "Test"
body = string.join(("From: %s" % From,
                    "To: %s" % To,
                    "Subject: %s" %Subject,
                    text
                    ),"\r\n")
     
print body

ERROR IS:

C:\Python27>python.exe c:\ROUGH\addingsubtofrm.py
Traceback (most recent call last):
  File "c:\ROUGH\addingsubtofrm.py", line 12, in 
    body = string.join(("From: %s" % From,
AttributeError: 'module' object has no attribute 'join'

...

For some reason, I do not get any error when I try to run her code with Python 2.7.1 on Windows XP. That's okay, though. I can still help a little bit on the style.

Although join is part of the string module, it is also directly attached to strings. So instead of using string.join(items, separator), you could use separator.join(items). That's considered the standard way to join a list of items into a single string these days.

Subject = "Testmail"
To = "yeahright@nonotreallyawebsiteihope.com"
From = "yeahright@nonotreallyawebsiteihope.com"
text = "Test"
body = "\r\n".join(("From: %s" % From,
                    "To: %s" % To,
                    "Subject: %s" %Subject,
                    text
                    ))
print body

This probably answers her question, but I am apparently in the mood to spend a lot of time writing about Python basics. Sounds like blog gold to me.

There's a problem with body if you want to use it for an actual email message. There needs to be a blank line between the headers and the body. One way to do that is to use join twice: once to build the header block and again to create a properly laid-out email message.

Subject = "Testmail"
To = "yeahright@nonotreallyawebsiteihope.com"
From = "yeahright@nonotreallyawebsiteihope.com"

text = "Test"

header_block = "\r\n".join((
    "From: %s" % From,
    "To: %s" % To,
    "Subject: %s" % Subject
    ))

# A full email has a blank line between the header block and the message body
body = "\r\n\r\n".join((header_block, text))
print body

The header block still looks a little clumsy. I am sure there is a prettier way to generate it. When I look at how the header block is printed, I realize that it looks a lot like a Python dictionary. Does the code look any clearer if I use a dictionary?

headers = {
    "Subject": "Testmail",
    "To": "yeahright@nonotreallyawebsiteihope.com",
    "From": "yeahright@nonotreallyawebsiteihope.com"
}

text = "Test"

# Each line of a header block contains a single email header,
# which looks like "Header-Field: Header-Value"
header_block = "\r\n".join(("From: %s" % headers['From'],
                            "To: %s" % headers['To'],
                            "Subject: %s" % headers['Subject']))

# A full email has a blank line between the header block and the message body
body = "\r\n\r\n".join((header_block, text))

print body

Well, no. Not really. I think I'm actually typing more than I was before, and it's not really any easier to read. It's all that "From: %s" % headers['From']" nonsense.

`join` takes a sequence. I do not have to hand it a literal like we have been doing so far. Let's build a list of header lines, and *then* join them.

headers = {
    "Subject": "Testmail",
    "To": "yeahright@nonotreallyawebsiteihope.com",
    "From": "yeahright@nonotreallyawebsiteihope.com"
}

text = "Test"

# Each line of a header block contains a single email header,
# which looks like "Header-Field: Header-Value"
header_lines = []

for field, value in headers.items():
    header_line = "%s: %s" % (field, value)
    header_lines.append(header_line)
      
header_block = "\r\n".join(header_lines)

# A full email has a blank line between the header block and the message body
body = "\r\n\r\n".join((header_block, text))

print body

It is easier to read, even if it is a little longer. We are building a list of header lines by stepping through each of the key/value pairs that make up the headers dictionary. Oh, and don't worry about what order the items are printed in. That order doesn't matter in email messages.

One thing - and this is a little thing - is that it takes us four lines of code to build the list. Like I said, it's a little thing. But building lists like this is so common that Python provides powerful tools called list comprehensions, which can reduce those four lines into one.

headers = {
    "Subject": "Testmail",
    "To": "yeahright@nonotreallyawebsiteihope.com",
    "From": "yeahright@nonotreallyawebsiteihope.com"
}

text = "Test"

# Each line of a header block contains a single email header,
# which looks like "Header-Field: Header-Value"
header_lines = ["%s: %s" % (field, value) for (field, value) in headers.items()]  
header_block = "\r\n".join(header_lines)

# A full email has a blank line between the header block and the message body
body = "\r\n\r\n".join((header_block, text))

print body

All right. Now if this were an actual email, there are some missing headers. There are probably also some details missing that are related to email handling. Rather than try to figure out what's missing, I'm going to suggest that you use the email library that comes standard with Python.

from email.mime.text import MIMEText

headers = {
    "Subject": "Testmail",
    "To": "yeahright@nonotreallyawebsiteihope.com",
    "From": "yeahright@nonotreallyawebsiteihope.com"
}

text = "Test"

msg = MIMEText(text)
for field, value in headers.items():
    msg[field] = value

print msg.as_string()

And what does the end result look like?

Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
To: yeahright@nonotreallyawebsiteihope.com
From: yeahright@nonotreallyawebsiteihope.com
Subject: Testmail

Test

There you go. If your end goal is generating emails, use the Python email library.