问熊猫series.str.split抛出错误如果展开=假，尽管只有一次分裂

EN

data = ['Swifter = ALL', 'COM-Swifter Testing & Monitoring = ALL',
   'Poll-Audit = ALL', 'Customer Relationship Management = ARC',
   'Credit Policy = ALL', 'CP-Credit Officers = ALL',
   'COM-Regulatory Swifter = ALL', 'Wrapper-Technology Wrapper = ABLM',
   'COM-Wrapper Assessments = ALL',np.nan,np.nan,np.nan]

df = pd.DataFrame(data=data,columns=['BASE'])
df


        BASE
0   Swifter = ALL
1   COM-Swifter Testing & Monitoring = ALL
2   Poll-Audit = ALL
3   Customer Relationship Management = ARC
4   Credit Policy = ALL
5   CP-Credit Officers = ALL
6   COM-Regulatory Swifter = ALL
7   Wrapper-Technology Wrapper = ABLM
8   COM-Wrapper Assessments = ALL
9   NaN
10  NaN
11  NaN

# 1
df[['BASE_TECH', 'BASE_TYPE']]= df['BASE'].str.split(' = ')

# 2
df[['BASE_TECH', 'BASE_TYPE']]= df['BASE'].str.split(' = ', n=1)

# 3
df[['BASE_TECH', 'BASE_TYPE']]= df['BASE'].str.split(' = ', n=2)


ValueError: Columns must be same length as key

# 4
df[['BASE_TECH', 'BASE_TYPE']]= df['BASE'].str.split(' = ', expand=True)

# 5
df[['BASE_TECH', 'BASE_TYPE']]= df['BASE'].str.split(' = ', n=1, expand=True)

# 6
df[['BASE_TECH', 'BASE_TYPE']]= df['BASE'].str.split(' = ', n=2, expand=True)