159 lines
5.7 KiB
Markdown
159 lines
5.7 KiB
Markdown
# Python all()函数
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> 原文：<https://www.pythonforbeginners.com/basics/python-all-function>
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在 python 中，我们通常使用比较运算符和逻辑运算符来检查不同数量元素的条件。如果您必须检查元素列表中的条件，该怎么办？在本文中，我们将讨论 python 中的`all()` 函数。我们还将看到如何对不同的可迭代对象使用`all()`函数。
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## Python 中的`all()`函数是什么？
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`all()`函数用于检查一个 iterable 对象中的所有元素是否都等于`True`。`all()`函数将列表、元组、集合、字典或字符串等可迭代对象作为其输入参数。执行后，如果 iterable 的所有元素的值都是`True`，它将返回`True`。否则返回`False`。您可以在下面的示例中观察到这一点。
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```py
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myList1 = [1, 2, 3, 4]
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myList2 = [1, True, False]
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myList3 = []
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print("The list is:", myList1)
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output = all(myList1)
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print("All the elements of the list evaluate to True:", output)
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print("The list is:", myList2)
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output = all(myList2)
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print("All the elements of the list evaluate to True:", output)
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print("The list is:", myList3)
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output = all(myList3)
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print("All the elements of the list evaluate to True:", output)
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```
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输出:
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```py
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The list is: [1, 2, 3, 4]
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All the [elements of the list](https://www.pythonforbeginners.com/basics/find-the-index-of-an-element-in-a-list) evaluate to True: True
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The list is: [1, True, False]
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All the elements of the list evaluate to True: False
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The list is: []
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All the [elements of the list](https://www.pythonforbeginners.com/basics/find-the-index-of-an-element-in-a-list) evaluate to True: True
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```
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你可以把`all()`函数的工作理解为`and`操作符的一个应用。对于具有元素`element1, element2, element3,.... elementN`的可迭代对象，使用`all()`函数相当于执行语句 `element1 AND element2 AND element3 AND ….., AND elementN`。
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## 带有 iterable 对象的 all()函数
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当我们将一个列表作为输入参数传递给 all()函数时，如果列表的所有[元素的值都为 True，那么它将返回 True。](https://www.pythonforbeginners.com/basics/find-the-index-of-an-element-in-a-list)
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```py
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myList1 = [1, 2, 3, 4]
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myList2 = [1, True, False]
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myList3 = []
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print("The list is:", myList1)
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output = all(myList1)
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print("All the elements of the list evaluate to True:", output)
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print("The list is:", myList2)
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output = all(myList2)
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print("All the elements of the list evaluate to True:", output)
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print("The list is:", myList3)
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output = all(myList3)
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print("All the elements of the list evaluate to True:", output)
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```
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输出:
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```py
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The list is: [1, 2, 3, 4]
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All the elements of the list evaluate to True: True
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The list is: [1, True, False]
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All the elements of the list evaluate to True: False
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The list is: []
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All the elements of the list evaluate to True: True
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```
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当我们将一个空列表传递给`all()` 函数时，它返回`True`。但是，如果列表中有一个元素的值为`False`，那么`all()`函数将返回`False`。
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当我们将任何字符串作为输入参数传递给`all()` 函数时，它返回`True`。
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```py
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myStr1 = "PythonForBeginners"
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myStr2 = ""
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print("The string is:", myStr1)
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output = all(myStr1)
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print("The output is:", output)
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print("The string is:", myStr2)
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output = all(myStr2)
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print("The output is:", output)
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```
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输出:
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```py
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The string is: PythonForBeginners
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The output is: True
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The string is:
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The output is: True
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```
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对于空字符串，`all()`函数返回`True`。
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类似于列表，当我们将一个集合作为输入参数传递给`all()`函数时，如果该集合的所有元素的值都为`True`，它将返回`True`。
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```py
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mySet1 = {1, 2, 3, 4}
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mySet2 = {1, 2, True, False}
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mySet3 = set()
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print("The Set is:", mySet1)
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output = all(mySet1)
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print("All the elements of the set evaluate to True:", output)
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print("The Set is:", mySet2)
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output = all(mySet2)
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print("All the elements of the set evaluate to True:", output)
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print("The Set is:", mySet3)
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output = all(mySet3)
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print("All the elements of the set evaluate to True:", output)
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```
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输出:
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```py
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The Set is: {1, 2, 3, 4}
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All the elements of the set evaluate to True: True
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The Set is: {False, 1, 2}
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All the elements of the set evaluate to True: False
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The Set is: set()
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All the elements of the set evaluate to True: True
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```
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当我们将一个空集传递给`all()`函数时，它返回`True`。
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## Python 中带字典的 all()函数
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当我们将一个字典作为输入参数传递给`all()` 函数时，如果 [python 字典](https://www.pythonforbeginners.com/dictionary/how-to-use-dictionaries-in-python/)的所有键都评估为`True`，它将返回`True`。否则返回`False`。
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```py
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myDict1 = {1: 1, 2: 2, 3: 3, True: 4}
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myDict2 = {False: 1, 1: 2, True: False}
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myDict3 = {}
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print("The Dictionary is:", myDict1)
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output = all(myDict1)
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print("All the keys of the dictionary evaluate to True:", output)
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print("The Dictionary is:", myDict2)
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output = all(myDict2)
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print("All the keys of the dictionary evaluate to True:", output)
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print("The Dictionary is:", myDict3)
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output = all(myDict3)
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print("All the keys of the dictionary evaluate to True:", output)
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```
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输出:
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```py
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The Dictionary is: {1: 4, 2: 2, 3: 3}
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All the keys of the dictionary evaluate to True: True
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The Dictionary is: {False: 1, 1: False}
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All the keys of the dictionary evaluate to True: False
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The Dictionary is: {}
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All the keys of the dictionary evaluate to True: True
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```
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当我们将一个空字典传递给`all()`函数时，它返回 True。
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## 结论
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在本文中，我们讨论了 python 中的 all()函数。我们还对不同的可迭代对象使用了`all()`函数，并观察了函数的输出。要了解更多关于 python 编程的知识，你可以在[列表理解](https://www.pythonforbeginners.com/basics/list-comprehensions-in-python)上阅读这篇文章。 |