python - 将数据附加到 Pandas 全局数据框变量不会持久

Question

我正在尝试使用 pandas dataframe 全局变量。但是，当我尝试将数据框重新分配或附加到全局变量时，数据框是空的。任何帮助表示赞赏。

import pandas as pd

df = pd.DataFrame()

def my_func():

    global df

    d = pd.DataFrame()

    for i in range(10):
        dct = {
            "col1": i,
            "col2": 'value {}'.format(i)    
        }

        d.append(dct, ignore_index=True) 
        # df.append(dct, ignore_index=True) # Does not seem to append anything to the global variable
    df = d # does not assign any values to the global variable

my_func()

df.head()

Answer 1

与list.append相反，pandas.DataFrame.append不是就地操作。稍微改变一下你的代码就可以按预期工作:

import pandas as pd

df = pd.DataFrame()

def my_func():
    global df
    d = pd.DataFrame()
    for i in range(10):
        dct = {
            "col1": i,
            "col2": 'value {}'.format(i)}
        d = d.append(dct, ignore_index=True) # <<< Assignment needed
        # df.append(dct, ignore_index=True) # Does not seem to append anything to the global variable
    df = d # does not assign any values to the global variable

my_func()

df.head()

输出:

   col1     col2
0   0.0  value 0
1   1.0  value 1
2   2.0  value 2
3   3.0  value 3
4   4.0  value 4