95 lines
2.6 KiB
Markdown
95 lines
2.6 KiB
Markdown
### type 和 isinstance 区别
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- type（）不会认为子类是一种父类类型。
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- isinstance（）会认为子类是一种父类类型。
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```python
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>>> class A:
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... pass
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...
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>>> class B(A):
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... pass
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...
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>>> isinstance(A(), A)
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True
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>>> type(A()) == A
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True
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>>> isinstance(B(), A)
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True
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>>> type(B()) == A
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False
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```
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### 删除变量定义
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- del
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- 通过使用 del 语句删除单个或多个对象
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```python
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>>> a = 1
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>>> a
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1
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>>> del a
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>>> a
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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NameError: name 'a' is not defined
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>>>
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```
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### 模块 `__name__`
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- 区分是自身运行还是被作为模块导入
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```python
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#!/usr/bin/python3
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# Filename: using_name.py
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if __name__ == '__main__':
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print('程序自身在运行')
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else:
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print('我来自另一模块')
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```
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### dir 函数
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- 内置的函数 dir() 可以找到模块内定义的所有名称。以一个字符串列表的形式返回
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```python
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>>> import module_support
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>>> dir(module_support)
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['__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'add']
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>>>
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>>> import sys
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>>> dir(sys)
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['__displayhook__', '__doc__', '__excepthook__', '__loader__', '__name__',
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'__package__', '__stderr__', '__stdin__', '__stdout__',
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'_clear_type_cache', '_current_frames', '_debugmallocstats', '_getframe',
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'_home', '_mercurial', '_xoptions', 'abiflags', 'api_version', 'argv',
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'base_exec_prefix', 'base_prefix', 'builtin_module_names', 'byteorder',
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'call_tracing', 'callstats', 'copyright', 'displayhook',
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'dont_write_bytecode', 'exc_info', 'excepthook', 'exec_prefix',
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'executable', 'exit', 'flags', 'float_info', 'float_repr_style',
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'getcheckinterval', 'getdefaultencoding', 'getdlopenflags',
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'getfilesystemencoding', 'getobjects', 'getprofile', 'getrecursionlimit',
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'getrefcount', 'getsizeof', 'getswitchinterval', 'gettotalrefcount',
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'gettrace', 'hash_info', 'hexversion', 'implementation', 'int_info',
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'intern', 'maxsize', 'maxunicode', 'meta_path', 'modules', 'path',
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'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1',
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'setcheckinterval', 'setdlopenflags', 'setprofile', 'setrecursionlimit',
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'setswitchinterval', 'settrace', 'stderr', 'stdin', 'stdout',
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'thread_info', 'version', 'version_info', 'warnoptions']
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```
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- 如果没有给定参数，那么 dir() 函数会罗列出当前定义的所有名称
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```python
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>>> dir()
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['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'a', 'answers', 'b', 'c', 'i', 'keyword', 'module_support', 'name', 'questions', 'random', 'str', 'student', 'tup', 'w', 'x', 'y']
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>>>
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```
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