python 如何以 Pythonic 的方式检测 CSV 文件中的缺失字段？
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How do I detect missing fields in a CSV file in a Pythonic way?
提问by bedwyr
I'm trying to parse a CSV file using Python's csvmodule (specifically, the DictReaderclass). Is there a Pythonic way to detect empty or missing fields and throw an error?
我正在尝试使用 Python 的csv模块（特别是DictReader类）解析 CSV 文件。是否有 Pythonic 方法来检测空字段或缺失字段并抛出错误？
Here's a sample file using the following headers: NAME, LABEL, VALUE
这是使用以下标题的示例文件：NAME、LABEL、VALUE
foo,bar,baz
yes,no
x,y,z
When parsing, I'd like the second line to throw an error since it's missing the VALUE field.
解析时，我希望第二行抛出错误，因为它缺少 VALUE 字段。
Here's a code snippet which shows how I'm approaching this (disregard the hard-coded strings...they're only present for brevity):
这是一个代码片段，它显示了我是如何处理这个的（忽略硬编码的字符串......它们只是为了简洁起见）：
import csv
HEADERS = ["name", "label", "value" ]
fileH = open('configFile')
reader = csv.DictReader(fileH, HEADERS)
for row in reader:
if row["name"] is None or row["name"] == "":
# raise Error
if row["label"] is None or row["label"] == "":
# raise Error
...
fileH.close()
Is there a cleaner way of checking for fields in the CSV file w/out having a bunch of ifstatements? If I need to add more fields, I'll also need more conditionals, which I would like to avoid if possible.
有没有一种更简洁的方法来检查 CSV 文件中的字段，而没有一堆if语句？如果我需要添加更多字段，我还需要更多条件，如果可能的话，我想避免这种情况。
回答by balpha
if any(row[key] in (None, "") for key in row):
# raise error
Edit: Even better:
编辑：更好：
if any(val in (None, "") for val in row.itervalues()):
# raise error
回答by Triptych
Since Noneand empty strings both evaluate to False, you should consider this:
由于None和空字符串都计算为False，因此您应该考虑：
for row in reader:
for header in HEADERS:
if not row[header]:
# raise error
Note that, unlike some other answers, you will still have the option of raising an informative, header-specific error.
请注意，与其他一些答案不同，您仍然可以选择提出信息丰富的、特定于标题的错误。
回答by John Millikin
This code will provide, for each row, a list of field names which are not present (or are empty) for that row. You could then provide a more detailed exception, such as "Missing fields: foo, baz".
此代码将为每一行提供该行不存在（或为空）的字段名称列表。然后，您可以提供更详细的异常，例如“缺少字段：foo, baz”。
def missing(row):
return [h for h in HEADERS if not row.get(h)]
for row in reader:
m = missing(row)
if missing:
# raise exception with list of missing field names
回答by retracile
Something like this?
像这样的东西？
...
for row in reader:
for column, value in row.items():
if value is None or value == "":
# raise Error, using value of column to say which field is missing
You may be able to use 'if not value:' as your test instead of the more explicit test you gave.
您可以使用“if not value:”作为您的测试，而不是您提供的更明确的测试。
回答by dalloliogm
If you use matplotlib.mlab.csv2rec, it already saves the content of the file into an array and raise an error if one of the values is missing.
如果您使用 matplotlib.mlab.csv2rec，它已经将文件内容保存到一个数组中，如果其中一个值丢失，则会引发错误。
>>> from matplotlib.mlab import csv2rec
>>> content_array = csv2rec('file.txt')
IndexError: list index out of range
The problem is that there is not a simple way to customize this behaviour, or to supply a default value in case of missing rows. Moreover, the error message is not very explainatory (could be useful to post a bug report here).
问题是没有一种简单的方法来定制这种行为，或者在缺少行的情况下提供默认值。此外，错误消息不是很有解释性（在此处发布错误报告可能很有用）。
p.s. since csv2rec saves the content of the file into a numpy record, it will be easier to get the values equal to None.
ps 因为 csv2rec 将文件的内容保存到一个 numpy 记录中，所以更容易获得等于 None 的值。
