How to extract particular key from the dict()? I have a dict() with 1000 keys. First 4 entries of dict are like. 

{
    'aaa': [1,0,6,8,0,5,9,1,1,0],
    'abc': [1,1,1,2,4,0,0,0,9,8],
    'cfg': [0,0,0,4,3,1,0,0,0,1],
    'cghjj': [7,8,9,2,3,0,0,0,0,0]
}


I want to create a dataset using each key one by one. I want to pick key1. Then create a dataset using function1 using the values of key1 and then pick key2. Creating another dataset using values of key2 and appending the result of key2 to key1 row-wise. Then with key3... and then append the result to the result of key1 and key2 and so on.. up to 1000 keys.

dataset=dict()

create_dataset:
    select values of key 1.
    b1=function1()
    b1=np.asarray(b1)

    then select key 2.
    b2=function1()
    b2=np.asarray(b2)

    np.append(b1,b2,axis=0)


...upto 1000 key.
You could iterate over all the keys and apply function1 to them and them append to the full_data_set. At the end you have all them concatenated. 

However, Python lists are unordered, so you don't control the order which keys are chosen.

data = {
    'aaa': [1, 0, 6, 8, 0, 5, 9, 1, 1, 0],
    'abc': [1, 1, 1, 2, 4, 0, 0, 0, 9, 8],
    'cfg': [0, 0, 0, 4, 3, 1, 0, 0, 0, 1],
    'cghjj': [7, 8, 9, 2, 3, 0, 0, 0, 0, 0]
}

def function1(l: list):
    # do something
    return l

full_data_set = []

for key in data.keys():
    full_data_set += function1(data[key])


If you do want to control the order of the keys, you need to make the ordered list of the keys somehow.

key_order = ['aaa', 'abc', 'cfg', 'cghjj']

data = {
    'aaa': [1, 0, 6, 8, 0, 5, 9, 1, 1, 0],
    'abc': [1, 1, 1, 2, 4, 0, 0, 0, 9, 8],
    'cfg': [0, 0, 0, 4, 3, 1, 0, 0, 0, 1],
    'cghjj': [7, 8, 9, 2, 3, 0, 0, 0, 0, 0]
}

def function1(l: list):
    # do something
    return l

full_data_set = []

for key in key_order:
    full_data_set += function1(data[key])