Python 3 Evaluate Variable in String

Question

Self admitted PHP coder turning to the Python side and my head hurts. I'm trying to do what I think would be simple. Read in a file (have that working) and then store each lines input into a variable then evaluate the string variable into an existing string of text.

Here's what I have:

with open('./users.txt') as users:
    for user in users:
        conn.request("GET", "/vmrest/users?query=(alias%2520is%2520{})".format(user), headers)
        res = conn.getresponse()
        data = res.read()

All I want is the value in my user variable to be placed right at the end of the string right after "/vmrest/users?query=(alias%2520is%2520user variable here", headers)

Thanks

EDIT Realized I didn't include what was happening sorry. Below is the feedback I get when executing.

Traceback (most recent call last):
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/http/client.py", line 885, in send
 self.sock.sendall(data)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/ssl.py", line 886, in sendall
v = self.send(data[count:])
TypeError: unhashable type: 'slice'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "amer-unity.py", line 12, in <module>
conn.request("GET", "/vmrest/users?query=(alias%2520is%2520{})".format(user), headers)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/http/client.py", line 1083, in request
self._send_request(method, url, body, headers)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/http/client.py", line 1128, in _send_request
self.endheaders(body)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/http/client.py", line 1079, in endheaders
self._send_output(message_body)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/http/client.py", line 913, in _send_output
self.send(message_body)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/http/client.py", line 889, in send
self.sock.sendall(d)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/ssl.py", line 886, in sendall
v = self.send(data[count:])
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/ssl.py", line 856, in send
return self._sslobj.write(data)
File "/opt/rh/rh-python35/root/usr/lib64/python3.5/ssl.py", line 581, in write
return self._sslobj.write(data)
TypeError: a bytes-like object is required, not 'str'

Your desired behavior is pretty clear, but I don't see any reason why your code shouldn't be working. What's the current behavior? (Side note: consider requests for sending web requests. It's much better than the Python standard lib.) — jpmc26
– jpmc26, Commented Jun 22, 2016 at 15:40
try printing out the formatted string and see what you get. it should be working. you'll also probably want to strip any surrounding whitespace from user (user.strip()) — acushner
– acushner, Commented Jun 22, 2016 at 15:49
So trying your request to just print the line: >>> with open('./users.txt') as users: ... for user in users: ... print("GET", "/vmrest/users?query=(alias%2520is%2520{})".format(user), headers) ... Traceback (most recent call last): File "<stdin>", line 3, in <module> NameError: name 'headers' is not defined >>> — rsaturns
– rsaturns, Commented Jun 22, 2016 at 15:59
It looks like the basic problem is that the request method is expecting a bytes instead of str, but that's a big guess on my part. A str is a text value, and unlike in Python 2.x, it can't be used as a byte sequence. I really recommend switching to requests and seeing if it just works; my suspicion is that it will sort of magically eliminate these kinds of problems. — jpmc26
– jpmc26, Commented Jun 22, 2016 at 15:59

jpmc26 · Accepted Answer · 2016-06-22 16:32:47Z

1

First, as @acushner suggests, you should strip your line:

"/vmrest/users?query=(alias%2520is%2520{})".format(user.strip())

This will remove any leading or trailing whitespace from the user string. Keep in mind that in Python, when you read a file's lines, it includes the line terminator (probably '\n' since you're on *nix). This will make sure it gets removed.

You might also want to skip empty lines:

user = user.strip()
if user:
    conn.request("GET", "/vmrest/users?query=(alias%2520is%2520{})".format(user), headers)
    # ...

If that doesn't fix it, I highly recommend switching to requests. It's a simpler library for sending web requests and receiving responses. It generally "just works" without much fuss. It's third party, so you need to install it first:

pip install requests

Then you would use it like this:

import requests

# ... some other code ...

with open('./users.txt') as users:
    for user in users:
        user = user.strip()
        if user:
            res = requests.get("/vmrest/users?query=(alias%2520is%2520{})".format(user.strip()), headers=headers)
            data = res.text

Note that there is zero set up code for establishing a connection; you just call the module method. It has some additional niceties as well, like parsing JSON:

data = res.json()

edited Jun 22, 2016 at 16:32

answered Jun 22, 2016 at 16:10

jpmc26

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2 Comments

rsaturns Over a year ago

Thank you this is now working and I can move on to my next challenges. You're definitely right requests is far superior to the basic http module. Not sure why Cisco uses that as their reference.

jpmc26 Over a year ago

@rsaturns requests has gotten a lot of traction in the Python community, but there's probably still a lot of people who don't know about it. Cisco could also have written their docs before it existed, or they might be uncomfortable with telling people to install a third party library in their official docs. Lots of possible reasons. Glad I could help, though.

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