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Python defaultdict class instantiation with default values


Python defaultdict class instantiation with default values

By : vishal
Date : November 22 2020, 04:01 AM
may help you . this occurs because defaults are evaluated precisely once when the function is defined, not every time it's called.
https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments
code :


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Python `defaultdict`: Use default when setting, but not when getting

Python `defaultdict`: Use default when setting, but not when getting


By : Jake
Date : March 29 2020, 07:55 AM
I hope this helps . Is there any way I can make a collections.defaultdict return a default constructed object when I set it... , I think that what you're looking for is something like this:
code :
>>> foo = {}
>>> foo.setdefault(3, []).append('dsafdasf') # Appends to default value
>>> foo[None] # Raises a KeyError exception
Javascript array with default values (equivalent of Python's defaultdict)?

Javascript array with default values (equivalent of Python's defaultdict)?


By : AntonF
Date : March 29 2020, 07:55 AM
This might help you No, this is not possible in JavaScript. Btw, you certainly meant Objects (property-value-maps) instead of arrays. Two solutions:
code :
function defaultDict(map, default) {
    return function(key) {
        if (key in map)
            return map[key];
        if (typeof default == "function")
            return default(key);
        return default;
    };
}

var a = defaultDict({cat: 1}, 0);
console.log(a('cat')); // 1
console.log(a('dog')); // 0
python: defaultdict with non-default argument

python: defaultdict with non-default argument


By : CodeMonkey
Date : March 29 2020, 07:55 AM
around this issue The defaultdict factory indeed does not take an argument.
You can create your own variant that does however; the trick is in defining a __missing__ method:
code :
class TestClassDict(dict):
    def __missing__(self, key):
        res = self[key] = TestClass(key)
        return res
>>> class TestClass(object):
...     def __init__(self, name):
...         self.name = name
...         self.state = 0
...     def getName(self):
...         self.state = self.state + 1
...         return "%s -- %i" % (self.name, self.state)
... 
>>> class TestClassDict(dict):
...     def __missing__(self, key):
...         res = self[key] = TestClass(key)
...         return res
... 
>>> db = TestClassDict()
>>> db['charlie'].getName()
'charlie -- 1'
>>> db
{'charlie': <__main__.TestClass object at 0x102f72250>}
Class instantiation with a dictionary parameter and class variables with default values

Class instantiation with a dictionary parameter and class variables with default values


By : user3538219
Date : March 29 2020, 07:55 AM
I hope this helps . I have a class whose __init__() takes a dictionary parameter. Each key in this dictionary corresponds to an instance variable. The instance variables have default values should we create this object without some or all of the dictionary keys. I have this coded as such: , Like this:
code :
def __init__(self, param1, dict_param):
    self.param1 = param1
    self.key1 = 10.0  # set default value
    # more defaults...

    for key, value in dict_param.iteritems():
        if hasattr(self, key):
           setattr(self, key, value)
def __init__(self, param1, dict_param):
    self.param1 = param1
    default_vals = {
        'key1': 'default 1',
        'key2': 'default 2',
        'etc': 'and so on'
    }

    for key, value in default_vals.iteritems():
        setattr(self, key, dict_param.get(key, value))
Python defaultdict: switching default creation on / off?

Python defaultdict: switching default creation on / off?


By : whiskeyremorse
Date : March 29 2020, 07:55 AM
I hope this helps you . Just use a regular dictionary instead. Simpler and works, since you only need the "default" functionality within a strictly limited context. In that limited context, use dict.setdefault:
code :
d = {}
for i in range(1, 10):
    d.setdefault(i, []).append(i+1)
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