using f-string with C-style string formatting in python

Question

I would like to write a function to build a bytes type string that need to use f-string with different value. the only way I can think about is like following code. anyone have better suggestion? In code, I have string like I have level but in my actual code the string is about 600 charactors

def get_level_string(x): size = dict(v1=1, v2= 200, v3= 30000) s = size.get('v1') name = lambda x: f"I have level value as {x} in the house" return { 'level1': b'%a' % (name(size['v1'])), 'level2': b'%a' % (name(size['v2'])), 'level3': b'%a' % (name(size['v3'])), }[x] a = get_level_string('level1') b = get_level_string('level2') c = get_level_string('level3') print(a, type(a)) print(b, type(b)) print(c, type(c)) => #b"'I have level value as 1 in the house'" <class 'bytes'> => #b"'I have level value as 200 in the house'" <class 'bytes'> => #b"'I have level value as 30000 in the house'" <class 'bytes'>

Why not just .encode() the string? e.g. lambda x: f"<blah> ... {x} ...".encode() and then you just have 'level': name(size['v1']) — AChampion
– AChampion, Commented Aug 10, 2018 at 18:00

Patrick Haugh · Accepted Answer · 2018-08-10 18:00:52Z

You can make this a good deal simpler, by generating the strings and then calling their encode method to make them bytes objects. Note that your function really just builds a dictionary and then looks stuff up in it. It's much simpler to build the dictionary only once and then supply the bound __getitem__ method under a different name.

template = "I have level value as {} in the house" size_list = (1, 200, 30000) sizes = {f"level{i}": template.format(x).encode() for i, x in enumerate(size_list, start=1)} get_level_string = sizes.__getitem__ # tests a = get_level_string('level1') b = get_level_string('level2') c = get_level_string('level3') print(a, type(a)) print(b, type(b)) print(c, type(c))

prints

b'I have level value as 1 in the house' <class 'bytes'> b'I have level value as 200 in the house' <class 'bytes'> b'I have level value as 30000 in the house' <class 'bytes'>

for your tests

thx, but i should mention by output is not necessary in that sequence. update my question
@jacobcan118 I'm afraid I don't understand. Do you mean that the various leveln in your code are actually unrelated 600 character strings?
i mean my output is not necessary to be level1 to level3, it maybe get_level_string('level2'), get_level_string('level3'), get_level_string('level1') in random sequence
@jacobcan118 I still don't see the issue. __getitem__ doesn't affect the underlying dictionary, so i shouldn't matter what order you're calling them in.

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