How to check if a string in Python is in ASCII?

To check if a string consists entirely of ASCII characters in Python, we can use several methods. Here are some commonly used approaches:

Method 1: Using the isascii() method of strings

In Python 3.7 and above versions, the string type provides an isascii() method. This method checks whether all characters in the string are ASCII characters. If they are, it returns True; otherwise, it returns False.

python
def is_ascii(s):
    return s.isascii()

# Example
string = "Hello"
print(is_ascii(string))  # Output: True

string = "你好"
print(is_ascii(string))  # Output: False

Method 2: Using the ord() function to verify character encoding

The ASCII character encoding range is 0 to 127. We can iterate over each character in the string, use the ord() function to obtain the ASCII value, and verify that this value falls within the range of 0 to 127.

python
def is_ascii(s):
    return all(ord(c) <= 127 for c in s)

# Example
string = "Hello"
print(is_ascii(string))  # Output: True

string = "Café"
print(is_ascii(string))  # Output: False

Method 3: Exception handling

Attempt to encode the string as ASCII. If successful, the string is considered entirely ASCII; if a UnicodeEncodeError exception is raised, it indicates the presence of non-ASCII characters.

python
def is_ascii(s):
    try:
        s.encode('ascii')
        return True
    except UnicodeEncodeError:
        return False

# Example
string = "Hello"
print(is_ascii(string))  # Output: True

string = "Español"
print(is_ascii(string))  # Output: False

Among these three methods, using the isascii() method is the most concise and efficient. However, note that it is only available in Python 3.7 and above versions. Other methods are compatible with all Python versions. In practical applications, we typically select the most suitable method based on the Python environment and specific requirements.