In [1]:

    

d = {'key1': 'aaa', 'key2': 'aaa', 'key3': 'bbb'}


    

In [2]:

    

value = d['key1']
print(value)


    

    




aaa

In [3]:

    

keys = [k for k, v in d.items() if v == 'aaa']
print(keys)


    

    




['key1', 'key2']

In [4]:

    

keys = [k for k, v in d.items() if v == 'bbb']
print(keys)


    

    




['key3']

In [5]:

    

keys = [k for k, v in d.items() if v == 'xxx']
print(keys)


    

    




[]

In [6]:

    

key = [k for k, v in d.items() if v == 'aaa'][0]
print(key)


    

    




key1

In [7]:

    

key = [k for k, v in d.items() if v == 'bbb'][0]
print(key)


    

    




key3

In [8]:

    

# key = [k for k, v in d.items() if v == 'xxx'][0]
# print(key)
# IndexError: list index out of range


    

In [9]:

    

def get_keys_from_value(d, val):
    return [k for k, v in d.items() if v == val]


    

In [10]:

    

keys = get_keys_from_value(d, 'aaa')
print(keys)


    

    




['key1', 'key2']

In [11]:

    

def get_key_from_value(d, val):
    keys = [k for k, v in d.items() if v == val]
    if keys:
        return keys[0]
    return None


    

In [12]:

    

key = get_key_from_value(d, 'aaa')
print(key)


    

    




key1

In [13]:

    

key = get_key_from_value(d, 'bbb')
print(key)


    

    




key3

In [14]:

    

key = get_key_from_value(d, 'xxx')
print(key)


    

    




None

In [15]:

    

d_num = {'key1': 1, 'key2': 2, 'key3': 3}


    

In [16]:

    

keys = [k for k, v in d_num.items() if v >= 2]
print(keys)


    

    




['key2', 'key3']

In [17]:

    

keys = [k for k, v in d_num.items() if v % 2 == 1]
print(keys)


    

    




['key1', 'key3']

In [18]:

    

d_str = {'key1': 'aaa@xxx.com', 'key2': 'bbb@yyy.net', 'key3': 'ccc@zzz.com'}


    

In [19]:

    

keys = [k for k, v in d_str.items() if v.endswith('com')]
print(keys)


    

    




['key1', 'key3']