List to Dictionary

a = ['a1','a2','a3','a4']
b = ['b1','b2','b3']
d = zip(a,b)
print(dict(d))  # {'a1': 'b1', 'a2': 'b2', 'a3': 'b3'}

Use counter to obtain a aggregated form from List

from collections import Counter
counter_dic = Counter(counter_list)

Dictionary to List

list(dit) # key

list(dit.values())  # value

List to Numpy array

import numpy as np
np.array(mylist)

Numpy array to List

list(nparray)

nparray.tolist()

String to int or the reverse

int(string)

str(int)

String to list

li=['a','b','c']
print(' '.join(str(i) for i in li))

Notice that List will store the address, thus it can contain different types. For np array, all elements are the same type.