对于Django解决方案(问题中没有提到):

from django.utils.text import Truncator
value = Truncator(value).chars(75)

看看Truncator的源代码来理解这个问题: https://github.com/django/django/blob/master/django/utils/text.py#L66

关于Django的截断: Django HTML截断

正则表达式:

re.sub(r'^(.{75}).*$', '\g<1>...', data)

长字符串被截断:

>>> data="11111111112222222222333333333344444444445555555555666666666677777777778888888888"
>>> re.sub(r'^(.{75}).*$', '\g<1>...', data)
'111111111122222222223333333333444444444455555555556666666666777777777788888...'

较短的字符串永远不会被截断:

>>> data="11111111112222222222333333"
>>> re.sub(r'^(.{75}).*$', '\g<1>...', data)
'11111111112222222222333333'

通过这种方式，你还可以“切割”字符串的中间部分，这在某些情况下会更好:

re.sub(r'^(.{5}).*(.{5})$', '\g<1>...\g<2>', data)

>>> data="11111111112222222222333333333344444444445555555555666666666677777777778888888888"
>>> re.sub(r'^(.{5}).*(.{5})$', '\g<1>...\g<2>', data)
'11111...88888'

这个方法不使用任何if:

数据[:75]+布尔(数据[75:])*'.'

简单而简短的helper函数:

def truncate_string(value, max_length=255, suffix='...'):
    string_value = str(value)
    string_truncated = string_value[:min(len(string_value), (max_length - len(suffix)))]
    suffix = (suffix if len(string_value) > max_length else '')
    return string_truncated+suffix

使用例子:

# Example 1 (default):

long_string = ""
for number in range(1, 1000): 
    long_string += str(number) + ','    

result = truncate_string(long_string)
print(result)


# Example 2 (custom length):

short_string = 'Hello world'
result = truncate_string(short_string, 8)
print(result) # > Hello... 


# Example 3 (not truncated):

short_string = 'Hello world'
result = truncate_string(short_string)
print(result) # > Hello world

下面是一个简单的函数，它将从任意一侧截断给定字符串:

def truncate(string, length=75, beginning=True, insert='..'):
    '''Shorten the given string to the given length.
    An ellipsis will be added to the section trimmed.

    :Parameters:
        length (int) = The maximum allowed length before trunicating.
        beginning (bool) = Trim starting chars, else; ending.
        insert (str) = Chars to add at the trimmed area. (default: ellipsis)

    :Return:
        (str)

    ex. call: truncate('12345678', 4)
        returns: '..5678'
    '''
    if len(string)>length:
        if beginning: #trim starting chars.
            string = insert+string[-length:]
        else: #trim ending chars.
            string = string[:length]+insert
    return string

info = data[:min(len(data), 75)