How to use python to determine the case of letters

Method 1

Use the built-in functions isupper() and islower() in Python to determine whether a letter is an uppercase or lowercase letter.

# 获取用户输入
letter = input("请输入一个字母：")
 
# 判断字母是否为大写
if letter.isupper():
    print("该字母为大写字母。")
 
# 判断字母是否为小写
elif letter.islower():
    print("该字母为小写字母。")
 
# 如果既不是大写字母也不是小写字母，则输出错误信息
else:
    print("输入错误，请输入一个字母。")

The user enters a letter, and the program uses the isupper() and islower() functions to determine whether the letter is uppercase or lowercase, and outputs the corresponding information. If the user enters characters other than letters, the program will output an error message.

Method 2

Use ASCII code values ​​to determine the case of letters.

# 获取用户输入
letter = input("请输入一个字母：")
 
# 判断字母是否为大写
if ord(letter) >= 65 and ord(letter) <= 90:
    print("该字母为大写字母。")
 
# 判断字母是否为小写
elif ord(letter) >= 97 and ord(letter) <= 122:
    print("该字母为小写字母。")
 
# 如果既不是大写字母也不是小写字母，则输出错误信息
else:
    print("输入错误，请输入一个字母。")

Each character has a unique ASCII code value, which is the standard encoding system used to represent text characters. The ASCII code value range of English letters is 65 to 90 for uppercase letters, and 97 to 122 for lowercase letters.

Use Python's built-in function ord() to convert the input letters into the corresponding ASCII code value, and use conditional statements to determine the case of the letters.

Method 3

Use the alphabet in Python.

# 定义字母表
uppercase_letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
lowercase_letters = "abcdefghijklmnopqrstuvwxyz"
 
# 获取用户输入
char = input("请输入一个字母: ")
 
# 判断字符是否为大写字母
if char in uppercase_letters:
    print("输入的字母为大写字母")
# 判断字符是否为小写字母
elif char in lowercase_letters:
    print("输入的字母为小写字母")
# 如果输入的字符不是字母，则输出错误信息
else:
    print("输入的不是字母，请重新输入")

This program defines a string containing uppercase letters and lowercase letters, and then uses the in operator to determine whether the entered characters are included in the string. If the input characters are uppercase letters, the corresponding information is output; if they are lowercase letters, the corresponding information is output; otherwise, an error message is output.

Method 4

Use regular expressions.

# 导入re模块
import re
 
# 获取用户输入
letter = input("请输入一个字母：")
 
# 判断字母是否为大写
if re.match(r'[A-Z]', letter):
    print("该字母为大写字母。")
 
# 判断字母是否为小写
elif re.match(r'[a-z]', letter):
    print("该字母为小写字母。")
 
# 如果既不是大写字母也不是小写字母，则输出错误信息
else:
    print("输入错误，请输入一个字母。")

Use the re.match() function and regular expressions to match the upper and lower case of letters. If the letter is uppercase, it matches a string that starts with an uppercase letter; if the letter is lowercase, it matches a string that starts with a lowercase letter.

python uppercase and lowercase letter exchange

In the Python language, uppercase and lowercase letters can be exchanged by using strings. Strings are often one of the most commonly used variable types in the Python language. Its methods can be used to manipulate strings and implement various string operations, and the conversion of uppercase and lowercase letters can also be implemented using string methods. Here is a way to interchange uppercase and lowercase letters:

1. Use .upper() to convert lowercase letters in a string to uppercase letters.

2. Use .lower() to convert uppercase letters in the string to lowercase letters.

3. Use .swapcase() to convert uppercase letters in the string to lowercase letters, and convert lowercase letters to uppercase letters.

For example, the following code can convert the lowercase letters in the string to uppercase letters:

str = "hello world"
str_upper = str.upper()
print(str_upper)

The running result is: "HELLO WORLD"

At the same time, the following code can convert Convert the uppercase letters in the string to lowercase letters:

str = "HELLO WORLD"
str_lower = str.lower()
print(str_lower)

The running result is: "hello world"

Finally, the following code can convert the lowercase letters in the string to uppercase letters, and at the same time Convert uppercase letters to lowercase letters:

str = "Hello World"
str_swap = str.swapcase()
print(str_swap)

The running result is: "hELLO wORLD"

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