adii1823
124 lines
2.7 KiB
Python
124 lines
2.7 KiB
Python
# dicts.py
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>>> a = dict(A=1, Z=-1)
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>>> b = {'A': 1, 'Z': -1}
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>>> c = dict(zip(['A', 'Z'], [1, -1]))
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>>> d = dict([('A', 1), ('Z', -1)])
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>>> e = dict({'Z': -1, 'A': 1})
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>>> a == b == c == d == e # are they all the same?
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True # They are indeed
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# zip
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>>> list(zip(['h', 'e', 'l', 'l', 'o'], [1, 2, 3, 4, 5]))
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[('h', 1), ('e', 2), ('l', 3), ('l', 4), ('o', 5)]
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>>> list(zip('hello', range(1, 6))) # equivalent, more pythonic
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[('h', 1), ('e', 2), ('l', 3), ('l', 4), ('o', 5)]
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# basic
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>>> d = {}
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>>> d['a'] = 1 # let's set a couple of (key, value) pairs
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>>> d['b'] = 2
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>>> len(d) # how many pairs?
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2
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>>> d['a'] # what is the value of 'a'?
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1
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>>> d # how does `d` look now?
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{'a': 1, 'b': 2}
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>>> del d['a'] # let's remove `a`
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>>> d
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{'b': 2}
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>>> d['c'] = 3 # let's add 'c': 3
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>>> 'c' in d # membership is checked against the keys
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True
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>>> 3 in d # not the values
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False
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>>> 'e' in d
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False
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>>> d.clear() # let's clean everything from this dictionary
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>>> d
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{}
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# views
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>>> d = dict(zip('hello', range(5)))
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>>> d
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{'h': 0, 'e': 1, 'l': 3, 'o': 4}
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>>> d.keys()
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dict_keys(['h', 'e', 'l', 'o'])
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>>> d.values()
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dict_values([0, 1, 3, 4])
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>>> d.items()
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dict_items([('h', 0), ('e', 1), ('l', 3), ('o', 4)])
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>>> 3 in d.values()
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True
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>>> ('o', 4) in d.items()
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True
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# other methods
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>>> d
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{'h': 0, 'e': 1, 'l': 3, 'o': 4}
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>>> d.popitem() # removes a random item (useful in algorithms)
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('o', 4)
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>>> d
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{'h': 0, 'e': 1, 'l': 3}
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>>> d.pop('l') # remove item with key `l`
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3
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>>> d.pop('not-a-key') # remove a key not in dictionary: KeyError
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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KeyError: 'not-a-key'
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>>> d.pop('not-a-key', 'default-value') # with a default value?
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'default-value' # we get the default value
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>>> d.update({'another': 'value'}) # we can update dict this way
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>>> d.update(a=13) # or this way (like a function call)
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>>> d
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{'h': 0, 'e': 1, 'another': 'value', 'a': 13}
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>>> d.get('a') # same as d['a'] but if key is missing no KeyError
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13
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>>> d.get('a', 177) # default value used if key is missing
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13
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>>> d.get('b', 177) # like in this case
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177
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>>> d.get('b') # key is not there, so None is returned
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# setdefault
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>>> d = {}
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>>> d.setdefault('a', 1) # 'a' is missing, we get default value
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1
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>>> d
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{'a': 1} # also, the key/value pair ('a', 1) has now been added
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>>> d.setdefault('a', 5) # let's try to override the value
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1
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>>> d
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{'a': 1} # no override, as expected
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# setdefault example
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>>> d = {}
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>>> d.setdefault('a', {}).setdefault('b', []).append(1)
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>>> d
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{'a': {'b': [1]}}
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# union
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>>> d = {'a': 'A', 'b': 'B'}
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>>> e = {'b': 8, 'c': 'C'}
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>>> d | e
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{'a': 'A', 'b': 8, 'c': 'C'}
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>>> e | d
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{'b': 'B', 'c': 'C', 'a': 'A'}
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>>> {**d, **e}
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{'a': 'A', 'b': 8, 'c': 'C'}
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>>> {**e, **d}
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{'b': 'B', 'c': 'C', 'a': 'A'}
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>>> d |= e
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>>> d
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{'a': 'A', 'b': 8, 'c': 'C'}
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