Pass String Parameter into Class/Function (Python)

Question

If I have a class as such:

class Sample:
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

I can create an object by:

temp = Sample(a=100,b=100,c=100)

But what if I have:

my_str = "a=100,b=100,c=100"

How can I temp = Sample(my_str) properly?

This seems like an XY problem. Where do you get that string? — internet_user, Feb 17 '18 at 05:47
Some of these answers are recommending to use `eval`. While it is simple, [there are reasons why `eval` is discouraged.](https://stackoverflow.com/questions/1832940/why-is-using-eval-a-bad-practice) — Mateen Ulhaq, Feb 17 '18 at 09:43
`eval` is a to use , no for avoiding! it has proplems but when need must use it , — Nozar Safari, Feb 17 '18 at 12:44

score 4 · Answer 1 · answered Feb 17 '18 at 05:52

4

You can parse and eval the string like:

Code:

@classmethod
def from_str(cls, a_str):
    return cls(**eval("dict({})".format(a_str)))

Test Code:

class Sample:
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

    @classmethod
    def from_str(cls, a_str):
        return cls(**eval("dict({})".format(a_str)))

x = Sample.from_str("a=100,b=100,c=100")
print(x.a)

Results:

answered Feb 17 '18 at 05:52

Stephen Rauch

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How about `ast.literal_eval` instead? I guess formatting it to a dict is ok too. – pylang Feb 17 '18 at 05:55
@pylang [`ast.literal_eval`](https://docs.python.org/3/library/ast.html#ast.literal_eval) can't handle operators (like `=`). `ast.literal_eval('a=100')` raises `SyntaxError: invalid syntax`. – G_M Feb 17 '18 at 05:56

score 1 · Answer 2 · answered Feb 17 '18 at 06:16

1

use eval

temp = eval("Sample("+my_str+")")

answered Feb 17 '18 at 06:16

Nozar Safari

505
4
17

G_M · Answer 3 · 2018-02-17T19:19:45.027

Although it is definitely an option, using eval can be dangerous. Here is an option which is @StephenRauch's code just without using eval.

>>> class Sample:
...     def __init__(self, a, b, c):
...         self.a = a
...         self.b = b
...         self.c = c
... 
...     @classmethod
...     def from_str(cls, a_str):
...         result = {}
...         for kv in a_str.split(','):
...             k, v = kv.split('=')
...             result[k] = int(v)
...         return cls(**result)
... 
>>> x = Sample.from_str('a=100,b=100,c=100')
>>> x.a
100
>>> type(x.a)
<class 'int'>

CodeIt · Answer 4 · 2018-02-17T06:05:42.787

0

You can use the below code.

class Sample:
    def __init__(self, a, b, c):
        self.a = int(a)
        self.b = int(b)
        self.c = int(c)

mystr = "a=100,b=100,c=100"
temp = Sample(mystr.split(",")[0].split("=")[1],mystr.split(",")[1].split("=")[1],mystr.split(",")[2].split("=")[1])
print(temp.a)
print(temp.b)
print(temp.c)

See it in action here

edited Feb 17 '18 at 06:05

answered Feb 17 '18 at 05:53

CodeIt

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1

I don't understand the negative voting for my answer. – CodeIt Feb 17 '18 at 06:01
me too, yours and below ones same I guess - imma upvote you buddy – Ankush Rathi Feb 17 '18 at 06:07
@AnkushRathi Thanks. – CodeIt Feb 17 '18 at 06:09

score 0 · Answer 5 · edited Feb 17 '18 at 09:56

0

This works for me:

my_str = "a=100,b=100,c=100"                                                                                         

temp = Sample(int(my_str.split(',')[0].split('=')[1]),
               int(my_str.split(',')[1].split('=')[1]),
               int(my_str.split(',')[2].split('=')[1]))

print(temp.a)
# prints 100

print(temp.b)
# prints 100

print(temp.c)
# prints 100

edited Feb 17 '18 at 09:56

CodeIt

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answered Feb 17 '18 at 05:54

Vikram Hosakote

3,528
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Shouldn't `temp.a == 100` and not `temp.a == 'a=100'`? – G_M Feb 17 '18 at 05:55
But isn't it supposed to be an integer? You are returning `'100'` vs `100` – G_M Feb 17 '18 at 05:59
@DeliriousLettuce Thanks for the comment, edited it again :) How does it look now? – Vikram Hosakote Feb 17 '18 at 06:02

score 0 · Answer 6 · answered Apr 21 '23 at 12:56

0

You can simply put temp = Sample(100,100,100) the class will automatically interpret

a = 100
b = 100
c= 100

answered Apr 21 '23 at 12:56

Agyo Michael Agyo

1

Pass String Parameter into Class/Function (Python)

6 Answers6

Code:

Test Code:

Results: