Convert list to a string with double quotes

Question

For an external application I need to send a command as a string, like this:

["START", "1", "2", "3", "4", "STOP"]

Note the double quotes!

I create this command with the following function:

def create_command(amount):
 command = ["START"]
 list = create_list(amount)
 command += list
 command += ["STOP"]
 command = str(command ) 
 command = command.replace("\'", "\"")
 return command

And I create a list from a given number with the following function:

def create_list(data):
 list = []
 data = str(data)
 for letter in data:
 list.append(letter)
 return list

Is the a way to make both functions more pythonic and not so straightforward? I don't really like them now, they look a bit clumpsy and I think there must be a better way do the thing.

Answer 1

create_list is building a list of all the items in the string form of data. And so you can change it to:

def create_list(data):
 return list(str(data))

I find it easier to read create_command if you merge some of the lines together:

def create_command(amount):
 command = ["START"] + create_list(amount) + ["STOP"]
 return str(command).replace("\'", "\"")

And so you can merge the above two changes together:

def create_command(amount):
 command = ["START"] + list(str(amount)) + ["STOP"]
 return str(command).replace("\'", "\"")

---

Expanding further, rather than using str.replace you can use json.dumps to format the list. This has the benefit that it will escape ' and " characters for you, which your code doesn't correctly handle. (Thanks Mathias)

import json
def create_command(amount):
 command = ["START"] + list(str(amount)) + ["STOP"]
 return json.dumps(command)

• Arthur Tacca: You could also make composing the list a bit neater using iterable unpacking: ["START", *str(amount), "STOP"] (available since Python 3.5).
• jpmc26: Why on Earth is json buried at the bottom of your answer?
• Peilonrayz: @jpmc26 because my primary purpose is to review the code, and so I work my way up to the best code. It wouldn't make sense to go the other way.
• jpmc26: It makes sense for the best code to be the first thing a reader sees so that they don't get confused about where you're headed. It also makes it harder to miss the best code when doing an initial skim.
• Peilonrayz: @jpmc26 what you're suggesting sounds like you want me to promote people to just steal my code and not learn anything. I want people to learn something, and so won't make you suggested changes.

Answer 2

Don't overshadow built in functions

list is already a built in. When you would try to use list() later on you'd get an Error.

Alternative

You need to send a string. Instead of creating a list and then converting to a string you can build the string from the start.

def create_list(data):
 return ', '.join(['"{}"'.format(c) for c in str(data)])
def create_cmd(data):
 return '["START", {}, "STOP"]'.format(create_list(data))

• Alex.S: Oh, thanks! I don't actually use list as a name, I just changed the variable names for the question and absolutely forgot that there is a function with this name.
• Konrad Rudolph: Eh. list is an obvious name, and shadowing names in a small scope isn’t at all problematic. I agree with the rest of your answer.
• Ludisposed: @KonradRudolph Sure in this small scope it doesn't really matter, but it is not a good habit to get into. And is worth mentioning at a code review

Answer 3

The python json.dumps function from stdlib can do this for you.

from json import dumps
result = build_your_list() # ['a', 'b']
dumps(result) # '["a", "b"]'

EDIT: I only just noticed that using this was recommended at the bottom of an already existing answer - but I think this deserves a full answer. I consider it much cleaner than the potentially inaccurate string manipulation answers.