Return key and value dict from list with dicts using __str__

Question

I try create class, which will return values to pretty print. I found this post python __str__ for an object but I still can't understand how I can improve my class.

Here is my class:

class PrintList(): 
    def __init__(self,lista):
        self.lista=lista
    def __str__(self):
        if isinstance(x[0] in self.lista, dict):           #for dicts in list
            return ','.join(str(item),'->',str(item[x]) for x in item) for item in self.lista
        else:         # for variables in list
            return ','.join(str(x) for x in self.lista)

and bug in first return:

return ','.join(str(item),'->',str(item[x]) for x in item) for item in self.lista
                                                                 ^
SyntaxError: invalid syntax

I try get the following result: key_dict->value_dict, etc.

Answer 1

You definitely have an invalid syntax in your comprehension/generator expression.

You should have written the expression as follows

return ','.join("{}->{}".format(item, item[x]) for x in item for item in self.lista)

Offtopic

As @MartijnPieter, for str.join , its faster to use a list comprehension rather than a generator expression notably because it needs to generate the data before stitching them togeter (a two pass algorithm). Please refer list comprehension without [ ], Python