python - python 中的数组可见性

Question

简单的问题:我有这个代码:我想从 csv 包中使用 Dictreader 获取一行，我想将每个条目转换为 float 并将其放入数据数组中。扫描结束时我想打印数组的前 10 个元素。它给我带来了数组数据可见性的错误。

with open(train, "r") as traincsv:
    trainreader = csv.DictReader(traincsv)
    for row in trainreader:
        data = [float(row['Sales'])]
print(data[:10])

如果我像这样把打印放在 for 中

with open(train, "r") as traincsv:
    trainreader = csv.DictReader(traincsv)
    for row in trainreader:
        data = [float(row['Sales'])]
        print(data[:10])

它会打印所有条目，而不仅仅是 10 个。

Answer 1

每次在 for 循环中都会覆盖数据。这就是你的问题的根源。

请上传一个示例输入供我尝试，我会的，但我相信下面的内容将通过附加到 data 而不是覆盖它来解决您的问题。

此外，最好尽快离开 with block 。

# Open with block and leave immediately
with open(train, "r") as traincsv:
    trainreader = csv.DictReader(traincsv)

# Declare data as a blank list before iterations
data =[]

# Iterate through all of trainreader
for row in trainreader:
    data.append([float(row['Sales'])])

# Now it should print first 10 results
print(data[:10])

附加列表的方法:

data = data + [float(row['Sales'])]

data += [float(row['Sales'])]

data.append([float(row['Sales'])]