字符串str.count(chr)

    1. str1="ACTGATCG"
    2. str1.count("A")

    列表list：用collections.Counter模块

    1. from collections import Counter
    2. import pandas as pd
    4. wordcount = Counter(allwords)
    6. wordcount.most_common(10)
    7. print(wordcount.most_common(10))
    8. df = pd.DataFrame(wordcount.most_common(10),
    9.                     columns=['word', 'count'])
    10. print(df)

    numpy array

    1. b=a[:,0]
    2. np.sum(b=='x')