为什么在尝试附加Python时我的列表没有加入

Question

import csv
filename='songdata.csv'
reader=csv.reader(open(filename,'r'))
header=next(reader)

data=[]
for row in reader:
    # row=[Song, Artist, Year, Tempo, Hotness, Duration, Key, Loudness, Mode]
    Song=row[0]
    Artist=row[1]
    Year=int(row[2])
    Tempo=float(row[3])
    Hotness=float(row[4])
    Duration=float(row[5])
    Key=int(row[6])
    Loudness=float(row[7])
    Mode=int(row[8])
    data.append([Song, Artist, Year, Tempo, Hotness, Duration, Key, Loudness, Mode])

for tempo in data:
    p=[]
    p.append(tempo[3])
    print p

My CSV file has columns for Song, Artist, Year, Tempo, Hotness, Duration, Key, Loudness, Mode. I made an empty list and I am trying to append all of the float values that represent Tempo into this list, but I keep just getting a bunch of separate list values that represent each float. It seems like nothing was actually appended to p. I even tried flattening the result with a function I made a while back, but it didn't have any effect. Any suggestions?

Answer 1

for tempo in data:
    p=[]
    p.append(tempo[3])

doesn't make sense since p is reset every time in the loop. So move the init of p before the loop.

Better yet: use a list comprehension to avoid such bugs:

p = [tempo[3] for tempo in data]