我创建了以下课程。包、网站和评论都是字符串,distroDict 是一个(字符串,列表)字典。
class TableEntry(object):
def __init__(self, package, website, distroDict, comments):
self.package = package
self.website = website
self.distroDict = distroDict
self.comments = comments
我想使用 defaultdict(TableEntry) 制作一个 (string, TableEntry) 自定义字典。
tableDict = defaultdict(TableEntry)
entry = TableEntry(package, website, distroDict, comments)
tableDict[package].append(entry)
我希望包是键,入口对象是值。我可以使用条目对象中的值,但如果我尝试将其附加到 tableDict,我会收到以下错误。
Traceback (most recent call last):
File "wiki.py", line 151, in <module>
printMetaData(lines, f)
File "wiki.py", line 73, in printMetaData
tableDict[package].append(entry)
TypeError: __init__() takes exactly 5 arguments (1 given)
我还尝试过以下方法:
tableDict[package].append(TableEntry(package, website, distroDict, comments))
并且本质上收到相同的错误:
Traceback (most recent call last):
File "wiki.py", line 150, in <module>
printMetaData(lines, f)
File "wiki.py", line 73, in printMetaData
tableDict[package].append(TableEntry(package, website, distroDict, comments))
TypeError: __init__() takes exactly 5 arguments (1 given)
当您尝试从 defaultdict 获取某些内容时,它会返回您实例化它的
default_factory
的实例,在您的情况下是 TableEntry
,没有方法 append
。但这实际上不是您收到错误的原因。发生这种情况是因为当返回一个实例时,它也会被评估,并且由于 TableEntry
没有它需要的参数,Python 解释器会抱怨。但即使在 TableEntry
调用中给定了 defaultdict
参数,您也可能会得到 TypeError
,因为 defaultdict
需要使用可调用对象(而不是类的实例)来调用。
总之,你不能用不可调用的实例化 defaultdict 除非你使用子类。相反,你应该做这样的事情:
class TableEntry(object):
def add(self, package, website, distroDict, comments):
self.package = package
self.website = website
self.distroDict = distroDict
self.comments = comments
tableDict = defaultdict(TableEntry)
entry = ("package", "website", "distroDict", "comments")
tableDict["package"].add(*entry)
然后你可以这样做
tableDict["package"]["website"]
获取您写入 self.website
的字符串。
另一种方法是让
__init__
方法的参数为可选,并将条目对象直接分配给tableDict。
class TableEntry:
def __init__(self, package=None, website=None, distroDict=None, comments=None):
self.package = package
self.website = website
self.distroDict = distroDict
self.comments = comments
tableDict = defaultdict(TableEntry)
tableDict["package"] = TableEntry("package", "website", "distroDict", "comments")
要使用
defaultdict
,您需要在默认初始化的类中提供实际的默认值。否则,当您尝试访问它时,您将收到运行时错误。如果您立即手动初始化该值,则不需要 defaultdict
。
要解决问题的
tableDict[package].append(entry)
,您所需要的只是defaultdict(list)
:
tableDict = defaultdict(list)
entry = TableEntry(package, website, distroDict, comments)
tableDict[package].append(entry)
但这里有一些实际使用 defaultdicts 的示例,可以让您省去一些初始化检查和代码
dataclasses
:
from dataclasses import dataclass, field
from collections import defaultdict
from typing import Any, Dict, List
@dataclass
class TableEntry:
package: str = ""
website: str = ""
distroDict: Dict[str, Any] = field(default_factory=defaultdict)
comments: List[str] = field(default_factory=list)
tableDict = defaultdict(TableEntry)
tableDict["mytestexample"]
>>> TableEntry(package='', website='', distroDict='', comments=[])
这可能是 defaultdict 可用性的更完整示例,其中更改了一些名称以更多地与包依赖项列表相关:
from dataclasses import dataclass, field
from collections import defaultdict
from typing import Any, Dict, List
@dataclass
class DependencyEntry:
package: str
website: str
distroDict: Dict[str, Any] = field(default_factory=defaultdict)
comments: List[str] = field(default_factory=list)
@dataclass
class DependencyGroup:
dependency_count: int = 0
dependencies: List[DependencyEntry] = field(default_factory=list)
dependencyTable = defaultdict(DependencyGroup)
dependencyTable["mytestpackage"]
>>> DependencyGroup(dependency_count=0, dependencies=[])
dependencyTable["mytestpackage"].dependencies
>>> []
# add a new instance directly into the dependency list
dependencyTable["mytestpackage"].dependencies.append(
DependencyEntry("Test", "example.com", {"distroArch": "metadata"}, ["this is a comment"]))
dependencyTable["mytestpackage"].dependencies
>>> [DependencyEntry(package='Test', website='example.com', distroDict={'distroArch': 'metadata'}, comments=['this is a comment'])]