Python Pandas 列数

import pandas as pd

data = {
    'Name': ['Alice', 'Bob', 'Charlie', 'David'],
    'Age': [25, 30, 35, 40],
    'City': ['New York', 'Los Angeles', 'Chicago', 'Houston']
}

df = pd.DataFrame(data)
print(df)

      Name  Age         City
0    Alice   25     New York
1      Bob   30  Los Angeles
2  Charlie   35      Chicago
3    David   40      Houston

num_columns = df.shape[1]
print("Number of columns in DataFrame: ", num_columns)

Number of columns in DataFrame:  3

df['Country'] = ['USA', 'USA', 'USA', 'USA']
print(df)

      Name  Age         City Country
0    Alice   25     New York     USA
1      Bob   30  Los Angeles     USA
2  Charlie   35      Chicago     USA
3    David   40      Houston     USA

df.drop('Country', axis=1, inplace=True)
print(df)

      Name  Age         City
0    Alice   25     New York
1      Bob   30  Los Angeles
2  Charlie   35      Chicago
3    David   40      Houston

selected_columns = df[['Name', 'City']]
print(selected_columns)

      Name         City
0    Alice     New York
1      Bob  Los Angeles
2  Charlie      Chicago
3    David      Houston