python string format calling a function

Question

Is there a way to format with the new format syntax a string from a function call? for example:

"my request url was {0.get_full_path()}".format(request)

so it calls the function get_full_path function inside the string and not as a parameter in the format function.

EDIT: Here is another example that will probably show my frustration better, this is what I would like:

"{0.full_name()} {0.full_last_name()} and my nick name is {0.full_nick_name()}".format(user)

this is what I want to avoid:

"{0} and {1} and my nick name is {2}".format(user.full_name(), user.full_last_name(), user.full_nick_name())

Answer 1

Python 3.6 adds literal string interpolation, which is written with an f prefix. See PEP 0498 -- Literal String Interpolation.

This allows one to write

>>> x = 'hello'
>>> s = f'{x}'
>>> print(s)
hello

It should be noted that these are not actual strings, but represent code that evaluates to a string each time. In the above example, s will be of type str, with value 'hello'. You can't pass an f-string around, since it will be evaluated to the result str before being used (unlike str.format, but like every other string literal modifier, such as r'hello', b'hello', '''hello'''). (PEP 501 -- General purpose string interpolation (currently deferred) suggests a string literal that will evaluate to an object which can take substitutions later.)

Answer 2

Not sure if you can modify the object, but you could modify or wrap the object to make the functions properties. Then they would look like attributes, and you could do it as

class WrapperClass(originalRequest):
    @property
    def full_name(self):
        return super(WrapperClass, self).full_name()

"{0.full_name} {0.full_last_name} and my nick name is {0.full_nick_name}".format(user)

which IS legal.

Answer 3

Python does not directly support variable interpolation. This means that it lacks certain functionality (namely, function calling in strings) which other languages support.

So, there isn't really anything to say here other than no, you can't do that. That's just not how Python's formatting syntax works.

The best you have is this:

"my request url was {0}".format(request.get_full_path())

Answer 4

What about this very weird thing?

"my request url was %s and my post was %s"\
    % (lambda r: (r.get_full_path(), r.POST))(request)

Explanation:

1. Classic way of formatting
2. Lambda function which takes a request and returns a tuple with what you want
3. Call the lambda inline as arguments for your string.

I still prefer the way you're doing it.

If you want readability you can do this:

path, post = request.get_full_path(), request.POST
"my request url was {} and my post was {}".format(path, post)

Answer 5

So summary of methods would be

(base) [1]~ $ cat r.py
# user is dict:
user = {'full_name': 'dict joe'}
print('{0[full_name]}'.format(user))

# user is obj:
class user:
    @property
    def full_name(self):
        return 'attr joe'


print('{0.full_name}'.format(user()))


# Wrapper for arbitray values - as dict or by attr
class Getter:
    def __init__(self, src):
        self.src = src

    def __getitem__(self, k):
        return getattr(self.src, k, 'not found: %s' % k)

    __getattr__ = __getitem__


print('{0[foo]} - {0.full_name}'.format(Getter(user())))
(base) [1]~ $ python r.py
dict joe
attr joe
not found: foo - attr joe