Python - 在使用 pandas.DataFrame.append 时遇到问题

Question

Can someone please help me figure out why the quer.append(l) is not working? My query for 'quer' and 'l' seem to work correctly. quer returns 31 rows (all rows that are "YES" in the Hill column. And 'l' returns 9 rows (all rows that are "YES" in the Underwater column). I then try to append the two together, but that doesn't seem to be workings. The 'return quer' is just returning the 31 YES that are in the Hill column and is not appending the 'l' dataframe

CSV: https://docs.google.com/spreadsheets/d/1PjnN00bikJfY7mO3xt4nV5Ua1yOIsh8DycGqed6hWD8/edit?usp=sharing

Workflow: save the csv as Monsters.csv and python file in the same folder and run the python file

import pandas as pd
import os

abspath = os.path.abspath(__file__)
dname = os.path.dirname(abspath)
os.chdir(dname)

currentDir = os.getcwd()

data = pd.read_csv(r'Monsters.csv')

def biomes(biome):
        ind = 0
        for i in range(len(biome)):
            if i == 0:
                quer = data.query("{} == 'YES'".format(biome[ind]))
                print ("Hill:", quer)  # returns 31 rows
            if i > 0:
                l = data.query("{} == 'YES'".format(biome[ind]))
                quer.append(l)   #this append is not working
                print ("Underwater: ", l ) #returns 9 rows
            ind += 1
        return quer # returns 31 rows (only the Hill biome) for some reason.

print(biomes(["Hill", "Coast"]))

Answer 1

As per the official Pandas documentation , DataFrame.append() returns a new object - it does not modify the object it is being called on. As such, I believe your append() is creating a new DataFrame, but not assigning it anywhere.

Try replacing quer.append(l) with quer = quer.append(l) to resolve this.