Python: Logical judgment and operator examples

This is an article about Python, mainly introducing logical judgments and operators.

(1)

Logical judgment:

If you want to implement a complex functional program, logical judgment essential. The most basic standard for logical judgment: Boolean type.

The Boolean type has only two values: True and False, which correspond to 1 and 0 in the Python language.

Enter the following code in Pycharm, and you will get True or False feedback after running.

1 print(1 > 2)
2 print('m' in 'member')
3 print(7 >= 7)
4 print(3 != 3)

Here, we call the expression that can return a Boolean value a Boolean expression. There are many ways to express Boolean expressions, the following are mainly introduced.

(2)

1. Comparison operator:

If the comparison formula is true, Return True; if not true, return False.

Common comparison operators are as follows:

In addition to simple comparison of two values, comparison operators also support more complex comparisons.

(1) Multi-condition comparison:

You can assign a value to the variable a first, and then perform multi-condition comparison.

1 a = 3
2 print(1 < a < 5)

(2) Comparison of variables:

Assign values ​​to variable a and variable b respectively and perform comparison.

1 a = 3
2 b = 3
3 print(a != b)
4 
5 s1 = 'duwangdan'
6 s2 = 'DuWangDan'
7 print(s1 == s2)

(3) Comparison of function results:

1 print(abs(-1) > len('duwagndan'))
2 # abs()：返回输入参数的绝对值

There are some minor issues that need to be paid attention to in comparison operations:

Different typesObjectYou cannot use ">, >=, <, <=" for comparison, but you can use "==, !=" for comparison.

1 print(21 == len('duwangdan'))

As mentioned at the beginning of the article, True corresponds to 1 and False corresponds to 0. Look at the following example, False+True is actually equivalent to 0+1:

1 print(False + True > False + False)

2. Member operator:

The keyword of the member operator is "in" , determine whether an element is in a list. After running the following program, you can get the feedback results.

1 a = 1
2 b = 'beautiful'
3 album = [1,'beautifully',False,7]
4 # 创建列表，命名该列表为album
5 print(a in album)
6 print(b in album

When album=[], it means the list is empty.

If you want to add new content to the album, you can use the append method. After adding, the new content will be displayed at the end of the list.

1 album = [1,'beautifully',False,7]
2 album.append('Wow')
3 # 用append()方法在album中新增内容
4 print(album)

3. Identity operator:

The identity operator is used to compare whether two objects are the same object, and the "=" in the previous comparison operator =” is used to compare whether the values ​​of two objects are equal.

The identity operator is mainly judged by "is, is not".

1 a = 'duwangdan'
2 b = 'duwangdan'
3 print(a is b)
4 print(a is not b)

4. Boolean operators:

There are three kinds of Boolean operators in Python: and, or, not.

In the following example, the returned results are: False, True, and True.

1 print(1 > 2 and 1 > 0)
2 print(1 > 2 or 1 > 0)
3 print(not False)

The main content of this article ends here, and conditional control will be introduced later.

Operating environment: Python version, 3.6; PyCharm version, 2016.2; Computer: Ma

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