欢迎使用re！按如下方式使用sub模块：

import re                                                                                                            
                                                                                                                     
s1 = """I love to eat apple and                                                                                      
bananas but at the same time, I do                                                                                   
not like to eat oranges                                                                                              
and I am not a fan of vegetables.                                                                                    
                                                                                                                     
I also like to eat biscuits.                                                                                         
                                                                                                                     
Meanwhile, oddly enough, I have never liked                                                                          
ice creams or chocolates because I                                                                                   
am never a sweet-toothed.                                                                                            
"""                                                                                                                  
                                                                                                                     
new_s1 = re.sub("\n(?!\n)", " ", s1)                                                                                       
                                                                                                                     
print(new_s1)

简单的str.split可能就足够了：

text = '''\
I love to eat apple and
bananas but at the same time, I do
not like to eat oranges
and I am not a fan of vegetables.

I also like to eat biscuits.

Meanwhile, oddly enough, I have never liked
ice creams or chocolates because I
am never a sweet-toothed.'''

for group in text.split('\n\n'):
    print(group.replace('\n', ' '))
    print()

图纸：

I love to eat apple and bananas but at the same time, I do not like to eat oranges and I am not a fan of vegetables.

I also like to eat biscuits.

Meanwhile, oddly enough, I have never liked ice creams or chocolates because I am never a sweet-toothed.