How to get the variable names from the string for the format() method

Question

Lets say I have this line:

"My name is {name}".format(name="qwerty")

I know that the variable name is name and so I can fill it. But what if the word inside the {} always changes, like this:

"My name is {name}"
"My name is {n}"
"My name is {myname}"

I want to be able to do this:

"My name is {*}".format(*=get_value(*))

Where * is what ever word was given inside the {}

Hope I was clear.

EDIT:

def get_value(var):
    return mydict.get(var)

def printme(str):
    print str.format(var1=get_value(var1), var2=get_value(var2))

printme("my name is {name} {lastname}")
printme("your {gender} is a {sex}")

Having this, I can't hard code any of the variables inside printme function.

score 35 · Accepted Answer · answered Apr 03 '14 at 07:17

35

You can parse the format yourself with the string.Formatter() class to list all references:

from string import Formatter

names = [fn for _, fn, _, _ in Formatter().parse(yourstring) if fn is not None]

Demo:

>>> from string import Formatter
>>> yourstring = "My name is {myname}"
>>> [fn for _, fn, _, _ in Formatter().parse(yourstring) if fn is not None]
['myname']

You could subclass Formatter to do something more fancy; the Formatter.get_field() method is called for each parsed field name, for example, so a subclass could work harder to find the right object to use.

answered Apr 03 '14 at 07:17

Martijn Pieters

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But now, how do i use `names` in the `format` method to get all the values? – MichaelR Apr 03 '14 at 07:22
@MichaelR: How were you planning to pair up the names with values? You can always use `dict(zip(names, values))` to create a dictionary, provided you know many values you need to provide. – Martijn Pieters Apr 03 '14 at 07:24
@MichaelR: `yourstring.format(**dict(zip(names, values)))`. – Martijn Pieters Apr 03 '14 at 07:24
I wanted to use this: `yourstring.format([(i,get_value(i)) for i in names])` but it gives me an error for some reason :-\ – MichaelR Apr 03 '14 at 07:32
`get_value()` is a method defined on the `Formatter` class; I was talking about a more complex setup where you subclass that class to have `get_value()` do something different in your overridden method. Read the `Formatter` documentation for more details. – Martijn Pieters Apr 03 '14 at 08:42
I ment my `get_value` method ive written – MichaelR Apr 03 '14 at 09:33
1

Right; you'd still have to build a dictionary; `yourstring.format(**{i: get_value(i) for i in names})` if you are on Python 2.7 or newer. – Martijn Pieters Apr 03 '14 at 09:35

score 3 · Answer 2 · edited Aug 16 '21 at 08:53

3

Python 3.8 added an awesome solution for this using f-strings:

my_var = 123
print(f"{my_var = }")

Which will print

my_var = 123

edited Aug 16 '21 at 08:53

Flair

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answered Aug 15 '21 at 17:57

Andrew Wilson

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Nishant Nawarkhede · Answer 3 · 2014-04-03T07:16:01.183

1

You can use variable instead of name="querty"

name1="This is my name";

>>"My name is {name}".format(name=name1)

Output:

'My name is abc'

Another example ,

a=["A","B","C","D","E"]
>>> for i in a:
...     print "My name is {name}".format(name=i)

Output:

My name is A
My name is B
My name is C
My name is D
My name is E

edited Apr 03 '14 at 07:16

answered Apr 03 '14 at 07:10

Nishant Nawarkhede

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score 0 · Answer 4 · answered Dec 08 '20 at 14:56

def get_arg(yourstring):
    arg_list = []
    pin = False
    for ch in yourstring:
        if ch == "{":
            pin = True
        elif ch == "}":
            pin = False
            arg_list.append(text)
            text = ""
        elif pin:
            text +=ch
    return arg_list

score -1 · Answer 5 · answered Apr 03 '14 at 07:10

-1

Or an alternative is to use a function:

def format_string(name):
    return "My name is {name}".format(name="qwerty")

Then call it:

format_string("whatever")

answered Apr 03 '14 at 07:10

Mihai Zamfir

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score -1 · Answer 6 · answered Apr 03 '14 at 07:51

If your data is in a dictionary (according to your edited question) then you can use the dictionary as a parameter for format.

data = {'first_name': 'Monty',
        'last_name': 'Python'}

print('Hello {first_name}'.format(**data))
print('Hello {last_name}'.format(**data))

How to get the variable names from the string for the format() method

6 Answers6

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