如何打破 Python 中的一系列链式方法？
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How to break a line of chained methods in Python?
提问by Juliusz Gonera
I have a line of the following code (don't blame for naming conventions, they are not mine):
我有以下一行代码（不要怪命名约定，它们不是我的）：
subkeyword = Session.query(
Subkeyword.subkeyword_id, Subkeyword.subkeyword_word
).filter_by(
subkeyword_company_id=self.e_company_id
).filter_by(
subkeyword_word=subkeyword_word
).filter_by(
subkeyword_active=True
).one()
I don't like how it looks like (not too readable) but I don't have any better idea to limit lines to 79 characters in this situation. Is there a better way of breaking it (preferably without backslashes)?
我不喜欢它的样子（不太可读），但在这种情况下，我没有更好的主意将行数限制为 79 个字符。有没有更好的方法来打破它（最好没有反斜杠）？
采纳答案by sth
You could use additional parenthesis:
您可以使用额外的括号：
subkeyword = (
Session.query(Subkeyword.subkeyword_id, Subkeyword.subkeyword_word)
.filter_by(subkeyword_company_id=self.e_company_id)
.filter_by(subkeyword_word=subkeyword_word)
.filter_by(subkeyword_active=True)
.one()
)
回答by Ivo van der Wijk
Just store the intermediate result/object and invoke the next method on it, e.g.
只需存储中间结果/对象并在其上调用下一个方法，例如
q = Session.query(Subkeyword.subkeyword_id, Subkeyword.subkeyword_word)
q = q.filter_by(subkeyword_company_id=self.e_company_id)
q = q.filter_by(subkeyword_word=subkeyword_word)
q = q.filter_by(subkeyword_active=True)
subkeyword = q.one()
回答by Haozhun
According to Python Language Reference
You can use a backslash.
Or simply break it. If a bracket is not paired, python will not treat that as a line. And under such circumstance, the indentation of following lines doesn't matter.
根据Python Language Reference
您可以使用反斜杠。
或者干脆打破它。如果括号未配对，python 不会将其视为一行。在这种情况下，以下行的缩进无关紧要。
回答by minhee
You seems using SQLAlchemy, if it is true, sqlalchemy.orm.query.Query.filter_by()method takes multiple keyword arguments, so you could write like:
你似乎在使用 SQLAlchemy，如果是真的，sqlalchemy.orm.query.Query.filter_by()方法需要多个关键字参数，所以你可以这样写：
subkeyword = Session.query(Subkeyword.subkeyword_id,
Subkeyword.subkeyword_word) \
.filter_by(subkeyword_company_id=self.e_company_id,
subkeyword_word=subkeyword_word,
subkeyword_active=True) \
.one()
But it would be better:
但它会更好：
subkeyword = Session.query(Subkeyword.subkeyword_id,
Subkeyword.subkeyword_word)
subkeyword = subkeyword.filter_by(subkeyword_company_id=self.e_company_id,
subkeyword_word=subkeyword_word,
subkeyword_active=True)
subkeuword = subkeyword.one()
回答by pkoch
My personal choice would be:
我个人的选择是：
subkeyword = Session.query(
Subkeyword.subkeyword_id,
Subkeyword.subkeyword_word,
).filter_by(
subkeyword_company_id=self.e_company_id,
subkeyword_word=subkeyword_word,
subkeyword_active=True,
).one()
回答by Raymond Hettinger
This is a case where a line continuation character is preferred to open parentheses. The need for this style becomes more obvious as method names get longer and as methods start taking arguments:
在这种情况下，换行符优先于开括号。随着方法名称变得更长并且方法开始接受参数，对这种风格的需求变得更加明显：
subkeyword = Session.query(Subkeyword.subkeyword_id, Subkeyword.subkeyword_word) \
.filter_by(subkeyword_company_id=self.e_company_id) \
.filter_by(subkeyword_word=subkeyword_word) \
.filter_by(subkeyword_active=True) \
.one()
PEP 8 is intend to be interpreted with a measure of common-sense and an eye for both the practical and the beautiful. Happily violate any PEP 8 guideline that results in ugly or hard to read code.
PEP 8 旨在以常识和实用和美观的眼光来解释。高兴地违反任何导致难看或难以阅读的代码的 PEP 8 准则。
That being said, if you frequently find yourself at odds with PEP 8, it may be a sign that there are readability issues that transcend your choice of whitespace :-)
话虽如此，如果您经常发现自己与 PEP 8 不一致，这可能表明存在超出您选择的空白的可读性问题:-)
回答by árni St. Siguresson
It's a bit of a different solution than provided by others but a favorite of mine since it leads to nifty metaprogramming sometimes.
它与其他人提供的解决方案略有不同，但却是我的最爱，因为它有时会导致漂亮的元编程。
base = [Subkeyword.subkeyword_id, Subkeyword_word]
search = {
'subkeyword_company_id':self.e_company_id,
'subkeyword_word':subkeyword_word,
'subkeyword_active':True,
}
subkeyword = Session.query(*base).filter_by(**search).one()
This is a nice technique for building searches. Go through a list of conditionals to mine from your complex query form (or string-based deductions about what the user is looking for), then just explode the dictionary into the filter.
这是构建搜索的好方法。浏览一个条件列表，从您的复杂查询表单中挖掘（或基于字符串的关于用户正在查找的内容的推断），然后将字典分解到过滤器中。
回答by acgtyrant
I like to indent the arguments by two blocks, and the statement by one block, like these:
我喜欢将参数缩进两个块，将语句缩进一个块，如下所示：
for image_pathname in image_directory.iterdir():
image = cv2.imread(str(image_pathname))
input_image = np.resize(
image, (height, width, 3)
).transpose((2,0,1)).reshape(1, 3, height, width)
net.forward_all(data=input_image)
segmentation_index = net.blobs[
'argmax'
].data.squeeze().transpose(1,2,0).astype(np.uint8)
segmentation = np.empty(segmentation_index.shape, dtype=np.uint8)
cv2.LUT(segmentation_index, label_colours, segmentation)
prediction_pathname = prediction_directory / image_pathname.name
cv2.imwrite(str(prediction_pathname), segmentation)
