python 2.7.5中的str()vs repr()函数 [英] str() vs repr() functions in python 2.7.5

问题描述

python 2.7.5中str()和repr()函数之间的区别是什么?

关于python.org的解释:

str()函数用于返回相当人类可读的值的表示形式，而repr()则用于生成 可以由解释器读取的表示形式(如果没有等效语法，则强制为SyntaxError)

但是我不清楚.

一些例子:

>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'"      # repr is giving an extra double quotes
>>> str(1.0/7.0)
'0.142857142857'
>>> repr(1.0/7.0)
'0.14285714285714285'  # repr is giving value with more precision

所以我想知道以下内容

1. 何时应使用str()，何时应使用repr()?
2. 在哪种情况下我可以使用其中任何一个?
3. str()不能执行repr()做什么?
4. repr()不能做什么?

解决方案

我什么时候应该使用str()和什么时候应该使用repr()?

为最终用户创建输出时，几乎总是使用str().

repr()主要用于调试和探索.例如，如果您怀疑一个字符串中没有打印字符，或者一个浮点数有一个小的舍入错误，则repr()将显示给您； str()可能不会.

repr()在生成要粘贴到源代码中的文字时也很有用.它也可以用于持久性(与ast.literal_eval或eval一起使用)，但这不是一个好主意-如果您想要可编辑的持久性值，则JSON或YAML之类的东西会更好，并且您不打算要对其进行编辑，请使用泡菜.

2.在哪种情况下，我可以使用其中任何一个?

好吧，您可以在几乎任何地方使用它们.除上述内容外，您通常不应该使用它们.

3.str()不能执行repr()做什么?

让您输出适合最终用户使用的信息-并非总是如此(例如，str(['spam'，'eggs'])不太可能是您要放在GUI中的任何东西)，但更常见的是比repr().

4.repr()不能做什么

>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'"      # repr is giving an extra double quotes
>>> str(1.0/7.0)
'0.142857142857'
>>> repr(1.0/7.0)
'0.14285714285714285'  # repr is giving value with more precision

再次提供对调试有用的输出-并非总是如此(用户创建的类的实例的默认值很少有帮助)，但会尽可能地提供.

有时甚至会为您提供有效的Python文字或其他表达式的输出-但除了交互式探索之外，您几乎不想依赖它.

what is the difference between str() and repr() functions in python 2.7.5?

Explanation on python.org:

The str() function is meant to return representations of values which are fairly human-readable, while repr() is meant to generate representations which can be read by the interpreter (or will force a SyntaxError if there is no equivalent syntax)

But it wasn't clear for me.

some examples:

>>> s = 'Hello, world.'
>>> str(s)
'Hello, world.'
>>> repr(s)
"'Hello, world.'"      # repr is giving an extra double quotes
>>> str(1.0/7.0)
'0.142857142857'
>>> repr(1.0/7.0)
'0.14285714285714285'  # repr is giving value with more precision

so I want to know the following

1. When should I use str() and when should I use repr()?
2. In which cases I can use either of them?
3. What can str() do which repr() can't?
4. What can repr() do which str() can't?

解决方案

When should i use str() and when should i use repr() ?

Almost always use str() when creating output for end users.

repr() is mainly useful for debugging and exploring. For example, if you suspect a string has non printing characters in it, or a float has a small rounding error, repr() will show you; str() may not.

repr() can also be useful for generating literals to paste into your source code. It can also be used for persistence (with ast.literal_eval or eval), but this is rarely a good idea--if you want editable persisted values, something like JSON or YAML is much better, and if you don't plan to edit them, use pickle.

2.In which cases i can use either of them ?

Well, you can use them almost anywhere. You shouldn't generally use them except as described above.

3.What can str() do which repr() can't ?

Give you output fit for end-user consumption--not always (e.g., str(['spam', 'eggs']) isn't likely to be anything you want to put in a GUI), but more often than repr().

4.What can repr() do which str() can't

Give you output that's useful for debugging--again, not always (the default for instances of user-created classes is rarely helpful), but whenever possible.

And sometimes give you output that's a valid Python literal or other expression--but you rarely want to rely on that except for interactive exploration.

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