如何使用熊猫连接2个CSV文件，以使生成的CSV文件没有行索引？请参见下面的示例：
file1.csv
date type price amount
2017-09-02 00:00:01 b 0.279111 94000
2017-09-02 00:00:01 b 0.279 43800
2017-09-02 00:00:01 b 0.2789 6000
2017-09-02 00:00:01 b 0.278812 2000
2017-09-02 00:00:01 b 0.278 7250
file2.csv
date type price amount
2018-03-02 00:00:01 q 0.279111 1400
2018-05-01 00:00:01 q 0.279 3800
2017-09-02 00:00:01 q 0.2789 640
desired_file.csv
date type price amount
2017-09-02 00:00:01 b 0.279111 94000
2017-09-02 00:00:01 b 0.279 43800
2017-09-02 00:00:01 b 0.2789 6000
2017-09-02 00:00:01 b 0.278812 2000
2017-09-02 00:00:01 b 0.278 7250
2018-03-02 00:00:01 q 0.279111 1400
2018-05-01 00:00:01 q 0.279 3800
2017-09-02 00:00:01 q 0.2789 640
不是这样的
date type price amount
1 2017-09-02 00:00:01 b 0.279111 94000
2 2017-09-02 00:00:01 b 0.279 43800
3 2017-09-02 00:00:01 b 0.2789 6000
4 2017-09-02 00:00:01 b 0.278812 2000
5 2017-09-02 00:00:01 b 0.278 7250
6 2018-03-02 00:00:01 q 0.279111 1400
7 2018-05-01 00:00:01 q 0.279 3800
8 2017-09-02 00:00:01 q 0.2789 640
我的代码：
import pandas as pd
a = pd.read_csv("file1.csv")
b = pd.read_csv("file2.csv")
combined = pd.concat([a, b])
combined.to_csv("desired_file.csv")
谢谢：）