问题求助

徐福福

## Learning objectives

* Remember the rules of setting variable names in Python and in this course
* Solve a problem using what we have learned from week 2, including:
  * Conditional statements
  * Loops, including the use of the `break` statement
* Experience that while the tools we have learned so far allow us to solve many different problems, writing code using only those tools can be inefficient and difficult

---

## Background information

A valid variable name in Python has to follow the following rules:
1. It must be composed of letters (`a-zA-Z`), digits (`0-9`) and/or underscore `_` (see Note)
2. It cannot start with a digit
3. It must not be one of the Python keywords

In this course, we further impose the following rules:

4. No mixing case (either all letters used are lowercase (for variables that are supposed to vary), or all letters used are uppercase (for variables that are supposed to be constant))
5. Meaningful names

While it is difficult to check rule 5 ("meaningful" is situational), it is possible to check other rules by a program.
## Instructions

Consider a program doing the following:

> Get a variable name provided by a user. Check if the variable name fulfils the rules 1, 2 and 4 above. If that is the case, print `Valid`. If not, print `Invalid`

See the `"Examples"` below for more details. Note that you do not need to check for rule 3 (we will see how to do it in the future).

1. Write one string that satisfies (no need to consider rule 3):
  * _Only_ the rule 1: _____
  * _Only_ the rule 2: _____
  * _Only_ the rule 4: _____
  * All but not rule 1: _____
  * All but not rule 2: _____
  * All but not rule 4: _____
  * All 3 rules _and_ composed of letters, digits and underscore: _____
  * All 3 rules _and_ composed of underscore only: _____
  * All 3 rules _and_ composed of digits and underscore only: _____

2. Write your code in [src/variable_name.py](src/variable_name.py) to implement the program specified above

3. Check your program using the strings listed in (1) as inputs (no need to submit)

You are NOT allowed to use any functionality that we have not seen in the course. Essentially, you are not allowed to use indexing or string methods.

This question is relatively difficult.
* You may want to work with your classmates as a group to solve the problem
* Apply decomposition to break down the problem into smaller, more manageable sub-problems
* If you get stuck, feel free to ask your instructors or teachers for help. Alternatively, you can have a look at the hint file available on Moodle
* Even if you cannot fully solve this question, but if your program has some meaningful steps towards solving the original question, you may still get a good grade for this problem set

---

## Assumptions

* Assume the input from the user is not empty

---## Note

* Note that Python actually accepts some other characters like Γ, but we do not accept them in the course (nor in this question)

---

## Examples

Some examples with valid variable name inputs:
```
>>> Enter a variable name: _a
Valid
```
```
>>> Enter a variable name: _1
Valid
```
```
>>> Enter a variable name: num_students
Valid
```
```
>>> Enter a variable name: numst_udents
Valid
```

Some examples with invalid variable name inputs:
```
>>> Enter a variable name: *3
Invalid
```
```
>>> Enter a variable name: 2numst_udents
Invalid
```
```
>>> Enter a variable name: NumStudents
Invalid
```
```
>>> Enter a variable name: Γ
Invalid
```

Note here:
* `Enter a variable name: ` is the input prompt
* `Valid` and `Invalid` are the printouts
* `*3`, `_a`, `num_students`, etc. are inputs from users

求问大神们 这个代码怎么做 还是不太明白 谢谢

isdkz

这个问题需要实现一个程序，输入一个变量名，判断是否符合Python变量名的规则。具体来说，Python变量名需要满足以下几个规则：

1. 只能由字母、数字和下划线组成
2. 不能以数字开头
3. 不能是Python的关键字
4. 变量名要有意义
5. 变量名要按照规定的命名方式进行命名

对于这个问题，我们需要实现一个程序，输入一个变量名，判断是否符合规则1、2、4，如果符合则输出"Valid"，否则输出"Invalid"。具体的实现思路如下：

1. 首先，我们需要从用户那里获取一个变量名，可以使用input()函数实现。
2. 接着，我们需要判断这个变量名是否符合规则1、2、4。对于规则1，我们可以使用isalnum()函数判断变量名是否只由字母和数字组成；对于规则2，我们可以使用isdigit()函数判断变量名的第一个字符是否是数字；对于规则4，我们可以使用islower()和isupper()函数判断变量名是否符合大小写规定。
3. 最后，根据判断结果输出"Valid"或"Invalid"即可。

下面是代码实现：

1. name = input("Enter a variable name: ")
   
2. 
   
3. # 判断规则1、2、4
   
4. if name.isalnum() and not name[0].isdigit() and (name.islower() or name.isupper()):
   
5.     print("Valid")
   
6. else:
   
7.     print("Invalid")
   

复制代码

在代码中，我们首先使用input()函数获取用户输入的变量名，然后使用isalnum()函数判断变量名是否只由字母和数字组成，使用isdigit()函数判断变量名的第一个字符是否是数字，使用islower()和isupper()函数判断变量名是否符合大小写规定。最后根据判断结果输出"Valid"或"Invalid"即可。

对于题目中要求的1-9个字符串，可以使用上述代码进行测试。

陶远航

这个问题的关键在于理解Python变量命名规则，并使用条件语句和循环来检查用户输入的字符串是否满足这些规则。以下是一个可能的解决方案：

1. # 获取用户输入
   
2. variable_name = input("Enter a variable name: ")
   
3. 
   
4. # 初始化标志变量
   
5. is_valid = True
   
6. 
   
7. # 检查规则2：变量名不能以数字开头
   
8. if variable_name[0].isdigit():
   
9.     is_valid = False
   
10. 
    
11. # 检查规则1和4：变量名只能包含字母、数字和下划线，并且不能混合大小写
    
12. else:
    
13.     has_lowercase = False
    
14.     has_uppercase = False
    
15.     for char in variable_name:
    
16.         if char.islower():
    
17.             has_lowercase = True
    
18.         elif char.isupper():
    
19.             has_uppercase = True
    
20.         elif not char.isdigit() and char != '_':
    
21.             is_valid = False
    
22.             break
    
23.     if has_lowercase and has_uppercase:
    
24.         is_valid = False
    
25. 
    
26. # 打印结果
    
27. if is_valid:
    
28.     print("Valid")
    
29. else:
    
30.     print("Invalid")
    

复制代码

这段代码首先获取用户输入的变量名，然后使用条件语句和循环来检查这个变量名是否满足规则。如果变量名满足所有规则，那么is_valid标志变量将保持为True，否则将被设置为False。最后，根据is_valid的值打印出结果。

注意：这个代码使用了字符串的索引和方法，这可能超出了你的课程范围。如果你的课程不允许使用这些功能，你可能需要寻找其他方法来解决这个问题。
请注意，本回答来自GPT-4
如果问题已经解决，请设置最佳答案

Mike_python小

问题分析

这个问题要求我们设计一个程序，接受用户输入的变量名，检查该变量名是否符合Python变量名的规则。具体规则如下：

1. 变量名只能由字母（a-z、A-Z）、数字（0-9）和下划线（_）组成；
2. 变量名不能以数字开头；
3. 变量名不得是Python的关键字；
4. 变量名要求按照规定的命名规范，要么全部小写（表示可变变量），要么全部大写（表示常量）。

我们需要编写的程序应该能够根据用户输入的变量名，判断其是否符合上述规则，并作出相应的输出。

解决方案

我们可以按照以下步骤来解决这个问题：

1. 获取用户输入的变量名；
2. 检查变量名是否只包含合法字符（字母、数字、下划线）；
3. 检查变量名的第一个字符是否为字母；
4. 检查变量名是否为Python的关键字；
5. 判断变量名是否按照规范命名（全部小写或全部大写）；
6. 根据上述判断结果，输出相应的提示信息。

下面是代码实现：

2. # 获取用户输入的变量名
3. variable_name = input("Enter a variable name: ")
5. # 检查变量名是否只包含合法字符（字母、数字、下划线）
6. valid_characters = set("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_")
7. if not all(char in valid_characters for char in variable_name):
8.     print("Invalid")
9.     exit()
11. # 检查变量名的第一个字符是否为字母
12. if not variable_name[0].isalpha():
13.     print("Invalid")
14.     exit()
16. # 检查变量名是否为Python的关键字
17. keywords = ["False", "None", "True", "and", "as", "assert", "async", "await", "break", "class", "continue", "def",
18.             "del", "elif", "else", "except", "finally", "for", "from", "global", "if", "import", "in", "is", "lambda",
19.             "nonlocal", "not", "or", "pass", "raise", "return", "try", "while", "with", "yield"]
20. if variable_name in keywords:
21.     print("Invalid")
22.     exit()
24. # 判断变量名是否按照规范命名（全部小写或全部大写）
25. if variable_name.islower() or variable_name.isupper():
26.     print("Valid")
27. else:
28.     print("Invalid")

复制代码

希望这个代码能够帮助到你！如果有任何问题，请随时提问。

球一个最佳答案谢谢啦！这对我非常重要！