How to formatting a list into a string?

Question

I am trying to format a string in python that takes arguments as items from a list of names. The catch is, I want to print all the list items with double quotes and backslash and one after each other in the same string only. The code is:

list_names=['Alex', 'John', 'Joseph J']
String_to_pring='Hi my name is (\\"%s\\")'%(list_names)

The output should look like this:

'Hi my name is (\"Alex\",\"John\",\"Joseph J\")'

But instead, I keep getting like this:

'Hi my names is (\"['Alex','John','Joseph J']\")'

I've even tried using .format() and json.dumps() but still the same result.

Is there any way to print the desired output or can I only print each list item at a time?

Answer 1

Without changing much of your code, you could simply format the repr representation of the list that's converted into a tuple.

# proper way - this is what you actually want
list_names = ['Alex', 'John', 'Joseph J']
string_to_print = 'Hi my name is %s' % (repr(tuple(list_names)))
 
print(string_to_print)
# Hi my name is ('Alex', 'John', 'Joseph J')

If you want to get your exact output, just do some string replacing:

# improper way
list_names = ['Alex', 'John', 'Joseph J']
string_to_print = 'Hi my name is %s' % (repr(tuple(list_names)).replace("\'", '\\"'))
print(string_to_print)
# Hi my name is (\"Alex\", \"John\", \"Joseph J\")

_{if you're trying to pass string_to_print to some other place, just try the proper way first, it might actually work for you.}

---

If you were mindful enough, you'll find that the previous "improper way" contains a small bug, try this adding "Alex's house" into list_names, the output would look like this:

Hi my name is (\"Alex\", \"John\", \"Joseph J\", "Alex\"s house")

To take care of that bug, you'll need to have a better way of replacing, by using re.sub().

from re import sub
list_names = ['Alex', 'John', 'Joseph J', "Alex's house"]
string_to_print = 'Hi my name is %s' % (sub(r'([\'\"])(.*?)(?!\\1円)(1円)', r'\"2円\"', repr(tuple(list_names))))
print(string_to_print)

But if things like this wouldn't happen during your usage, I would suggest to keep using the "improper way" as it's a lot simpler.

• NightOwl19: I tried using the improper way and it really works. Why we are passing tuple as list names and not the actual lists?
• Taku: Lists are formatted with square brackets, but your expected output uses parentheses instead, which represents tuple. You can remove tuple(), but the output would change to "Hi my name is [\"Alex\", ...]"
• NightOwl19: With the replace function added after the tuple_names, the output I'm getting is: Hi my name is (\\"Alex\\", \\"John\\", \\"Joseph J\\"). The backslash is getting replaced with double backslashed and not the single.
• Taku: You're not using print(), what you're seeing is just the repr of tuple_names, it's for showing you that the double quotes are escaped. The actual string contains only one backslash. If you ran my code as-is, or write it to a file, you'll see that there's only one backslash.
• NightOwl19: Didn't consider the "Alex's House" scenario as I was just trying to print the first names only. But thanks for the upgrade.

Answer 2

There is no function for formatting lists as human-friendly strings You have to format lists yourself:

names = ",".join(r'\"{}\"'.format(name) for name in list_names)
print(names)
#\"Alex\",\"John\",\"Joseph J\"
print('Hi my name is ({})'.format(names))
#Hi my name is (\"Alex\",\"John\",\"Joseph J\")

• DYZ: To the downvoter: what's wrong with my suggested solution?
• NightOwl19: Your method works as well, thanks. Is it possible to follow same approach by passing arguments to %s as well?
• DYZ: %s is an old-style formatting mechanism and should be avoided pyformat.info

Answer 3

This is one way using format and join:

list_names = ['Alex', 'John', 'Joseph J']
String_to_pring='Hi my name is (\\"{}\\")'.format('\\",\\"'.join(i for i in list_names))
# Hi my name is (\"Alex\",\"John\",\"Joseph J\")