26.11.2019 Python

def reverse_dict(d):
    result = {}

    for x, y in d.items():
        if y not in result:
            result[y] = [x]
        else:
            result[y].add(x)
    return result

d = { 2:4, 3:9, 4:16, 5:25, 5:25, 4:16 }

inv_d = reverse_dict(d)

print(inv_d)
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from math import sin, asin, cos, acos, tan, atan

def update_inv(d):
    tmp = { key:item for key, item in d.items() }
    for key, item in tmp.items():
        d[item] = key
    pass

d = {sin: asin, cos: acos, tan: atan}
update_inv(d)

print(d)
------------------------------------------------
d.values()
d.items()
d.keys()
--------------------------------------------------
def update_inv(d):
#    tmp = { key:item for key, item in d.items() }
#    for key, item in tmp.items():
#        d[item] = key
    for k in list(d):
        d[d[k]] = k
    pass
--------------------------------------------------
def reverse_dict(d):
    result = {}

    for x, y in d.items():
        if y not in result:
            result[y] = x
        else:
            if result[y] > x:
                result[y] = x
    return result

d = { 2:4, 1:4, 3:9, 4:16, 4:25, 5:25, 4:16 }

print(reverse_dict(d))
---------------------------------------------------
len(set(d.values())) === len(d)