赋值前的全局变量和引用

您还必须在函数do_tuff_和_append_df()下声明“global df”。

因为函数do_stuff_和_append_df()不知道您是在引用局部变量还是全局变量。

更好的是, 不使用全局变量 . 将所需的数据帧作为参数传递。

from datetime import datetime
import pandas as pd

def do_stuff_and_append_df(df):
    dt = datetime.now()
    row = dict.fromkeys(df.columns.tolist())
    row['datetime'] = dt
    row['pduType'] = 'blah'
    df = df.append(row, ignore_index=True)
    print(df.head())
    return df

def main():
    # empty dataframe for appending
    header = ['datetime', 'pduType']
    df = pd.DataFrame(columns=header)
    # Main loop
    try:
        while True:
            df = do_stuff_and_append_df(df)

    except KeyboardInterrupt:
        print('\nSaving and exiting.')
        df.to_csv('data.csv')

main()

尝试在中添加全局声明 do_stuff_and_append_df

def do_stuff_and_append_df():
    global df

如果需要全局变量,请将其显式地放在全局范围中:

from datetime import datetime
import pandas as pd

def do_stuff_and_append_df():
    dt = datetime.now()
    row = dict.fromkeys(df.columns.tolist())
    row['datetime'] = dt
    row['pduType'] = 'blah'
    df = df.append(row, ignore_index=True)
    print(df.head())

def main():
    # Main loop
    try:
        while True:
            do_stuff_and_append_df()

    except KeyboardInterrupt:
        print('\nSaving and exiting.')
        df.to_csv('data.csv')

if __name__ == "__main__":
    header = ['datetime', 'pduType']
    df = pd.DataFrame(columns=header)

要么,要么看看切普纳的答案。你最好 不要 使用全局变量