Python, ValueError: not enough values to unpack (expected 2, got 1), Python OOP-CodePudding

In this project, i was told to make a code where i should leverage the convenience of a dictionary to power a configuration file.

My following code looks like this:

class ConfigDict(dict):

    def __init__(self, filename):
        self._filename = filename
        if os.path.isfile(self._filename):
            with open(self._filename) as fh:
                for line in fh:
                    line = line.rstrip()
                    key, value = line.split('=', 1)
                    dict.__setitem__(self, key, value)    

    def __setitem__(self, key, value):
        dict.__setitem__(self, key, value)
        with open(self._filename, 'w') as fh:
            for key, val in self.items():
                fh.write('{0}={1}\n'.format(key, val))

cd = ConfigDict("Config_file.txt")

The problem arises when i try to run the code, with the specified file name, An error of "ValueError: not enough values to unpack (expected 2, got 1)", from this line of code:

key, value = line.split('=', 1)

I have searched for solutions regarding this particular problem but have never seem to find it, and your help would really benefit me.

CodePudding user response：

First, it would be great if you could share a few sample lines from your input file.

The reason you get the error is because line.split('=', 1) is not returning two values (key and value). What solution to go for depends on what you intend to do with the file.

If you are expecting only 2 values, then keep the code as is and check your files. I see you already leverage the maxsplit argument, which determines the maximum times to split:

key, value = line.split("=", maxsplit=1).

This will not only ensure that only a single split is done but also that it returns a list with 2 elements (at most) or less. Less is the issue here since the line you are reading doesn't have that many. Could it be the headline or a line containing other info that cannot be parsed using split? This is important because if you have any corrupt line with more than a single "=" symbol, then a ValueError will be thrown:

line = "1=2=3"
key, value = line.split("=")
> ValueError: too many values to unpack (expected 2)

And if you have less, then you will get the error you cited above.

If you have some corrupt lines with only <= 1 value to split, then a good course of action would be to ignore such lines altogether with a try/except block:

class ConfigDict(dict):

def __init__(self, filename):
    self._filename = filename
    if os.path.isfile(self._filename):
        with open(self._filename) as fh:
            for line in fh:
                line = line.rstrip()
                try:
                   key, value = line.split('=', 1)
                   dict.__setitem__(self, key, value)
                except ValueError:
                   pass

The code above will only set key/value pairs if the split was successful.

Your code otherwise seems perfectly fine.

CodePudding user response：

This error is because of a corner case. Suppose line = 'apple', then key,value = line.split('=', 1) will throw error.Your code is expecting two values but this corner case will return only one value hence the error "Value Error: not enough values to unpack (expected 2, got 1)".