I'm trying to make a templated string that will print values of a given dict. However, the key may or may not exist in the dict. If it doesn't exist, I'd like it to return an empty string instead.
To demonstrate what I mean, let's say I have a dict:
test_dict = { 1: "a", 2: "b"}
And a template string:
'{} {} {}'.format(test_dict.get(1), test_dict.get(2), test_dict.get(3))
I'd like the following output:
'a b '
But instead I get:
'a b None'
Use the dictionary's get function. This allows you to specify a value to return if the key is not found
'{}, {}, {}'.format(test_dict.get(1,''), test_dict.get(2,''), test_dict.get(3, ''))
One way would be to get the length of the dict, and put the same amount of placeholeders inside the template:
In [27]: test_dict = { 1: "a", 2: "b"}
In [28]: ' '.join(['{}'] * len(test_dict))
Out[28]: '{} {}'
In [29]: ' '.join(['{}'] * len(test_dict)).format(*test_dict.values())
Out[29]: 'a b'
Note that, this is basically the same as ' '.join(test_dict.values()) but showing you the template string as an example.
UPDATES PER OP COMMENT
You can use the string library to help here. See the below script using your test_dict:
#https://stackoverflow.com/a/51359690
from string import Formatter
class NoneAsEmptyFormatter(Formatter):
def get_value(self, key, args, kwargs):
v = super().get_value(key, args, kwargs)
return ' ' if v is None else v
fmt = NoneAsEmptyFormatter()
test_dict = { 1: "a", 2: "b"}
test_str = fmt.format('{} {} {}', test_dict.get(1), test_dict.get(2), test_dict.get(3))
print(test_str)
We build a quick NoneAsEmptyFormatter class and use that to format the strings in coming from the dict.
None in the event that the key does not exist.
Re your comment,
Now that you mention the extra space though, is there a way to remove the placeholder completely if key doesn't exist?
Yes, this is possible. Just make a list of values, filter out any Nones, then join the result:
In [3]: values = map(test_dict.get, [1, 2, 3])
In [4]: ' '.join(v for v in values if v is not None)
Out[4]: 'a b'
Or if order is not important, or if you're using Python 3.7+ and you want to preserve insertion order, you can skip some steps:
In [5]: ' '.join(test_dict.values())
Out[5]: 'a b'
None..get()to specify a return value if the key is not found, instead of the defaultNone. Usetest_dict.get(3, '')and it will return a blank string.