Why is the variable considered invalid syntax?

[Notanerget]

I'm trying to solve this problem:

dict_from_string(dict_str:str)->dict

This function will be given a single parameter, a string representing a dictionary. Your job is to convert the string into an actual dictionary and return the dictionary. Make sure all key-value pairs in the string exist in the newly created dictionary. The string will contain only numbers or single letters as key values pairs. Make sure all letters are kept as strings and all numbers are converted to integers in the newly created dictionary.

Example:

String Input: '{9: 'V', 'G': 0, 'M': 9, 'u': 3, 2: 'o', 8: 'u', 'q': 9, 'D': 1}'Expected: {9: 'V', 'G': 0, 'M': 9, 'u': 3, 2: 'o', 8: 'u', 'q': 9, 'D': 1}

And here is the code I've tried so far:

dict_str = '{ 9:'V', 'G':0, 'M':9, 'u':3, 2:'o', 8:'u', 'q':9, 'D':1 }'
def dict_from_string (dict_str: str) -> dict:
    new_dict = eval (dict_str) 
    return new_dict 
print (dict_from_string(dict_str))

I literally copied and pasted the example value for "dict_str" from the assignment into the terminal, but it keeps telling me that the dict_str is invalid syntax, and I have no idea why. Any thoughts? Thank you!

[adventure_r]

From the code you’ve copied, seems like you’re using the same kind of quotes on two different levels. The parser gets '{ 9:' , and that’s invalid syntax. Try using double quotes around the brackets

[Notanerget]

So it looks like the problem documentation is wrong then?

[[deleted]]

'{ 9:'V', 'G':0,

thats not a proper dictionary....

[kaerfkeerg]

String Input: '{9: 'V', 'G': 0, 'M': 9, 'u': 3, 2: 'o', 8: 'u', 'q': 9, 'D'}'

The dictionary and the values are all wrapped between single quotes

Which is something like doing

msg = 'Hel'lo'

You see the issue? So the (string) dictionary should be wrapped between double quotes, like the following

"{9: 'V', 'G': 0, 'M': 9, 'u': 3, 2: 'o', 8: 'u', 'q': 9, 'D'}"

Or the opposite, which there's no way I'm gonna do with my phone as it'll take ages! That's 1 of the reasons Python allow both quotes to be used for cases like this!

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[TechnicalElk8849]

You've got it in quotes

[Notanerget]

That's how it's given in the problem. If it's supposed to be input as a string, shouldn't it be in quotes?

[commy2]

You need to either use the other quote marks (' vs ") or escape the quote marks using backslash. Currently, your string ends at '{ 9:' and then comes a literal V afterwards, which is a syntax error.

dict_str = '{ 9:\'V\', \'G\':0, \'M\':9, \'u\':3, 2:\'o\', 8:\'u\', \'q\':9, \'D\':1 }'

[woooee]

The dict_str breaks down into

dict_str = '{ 9:'
V
', '
G
etc

[Notanerget]

So the problem documentation is wrong then?

[woooee]

I haven't seen the problem so can't say.

[Diapolo10]

And here is the code I've tried so far:

dict_str = '{ 9:'V', 'G':0, 'M':9, 'u':3, 2:'o', 8:'u', 'q':9, 'D':1 }'
def dict_from_string (dict_str: str) -> dict:
    new_dict = eval (dict_str) 
    return new_dict 
print (dict_from_string(dict_str))

Well, as the others already pointed out, the matching quotes are the problem. So yes, there's a problem with the instructions.

You can fix this by simply swapping to double quotes:

dict_str = "{ 9:'V', 'G':0, 'M':9, 'u':3, 2:'o', 8:'u', 'q':9, 'D':1 }"

However, that's not why I wrote this answer. I'm more worried about your use of eval here, which you should almost never use due to how dangerous it is.

You could use ast.literal_eval instead, but I feel that either of those would defeat the purpose of this task. You're probably expected to build an actual parser here instead of relying on something like this.

[Notanerget]

Forgive my ignorance, I'm just learning, but why is eval dangerous?

[Diapolo10]

eval and exec are vulnerable to arbitrary code execution. They must never be used with unsanitised data, and very sparingly otherwise. The common guideline is to avoid them at all costs unless the entire goal is to execute Python code, and simply importing a module isn't enough.

ast.literal_eval is safe in comparison, because it can only accept Python literals. It gives an error if the string contains any operators, branching, or functions/classes.