Python列表加入-在开始或结尾处包含分隔符

Question

', '.join(['a', 'b', 'c', 'd'])的输出是：

a, b, c, d

Python中是否有标准方法来实现以下输出？

# option 1, separator is also at the start
, a, b, c, d

# option 2, separator is also at the end
a, b, c, d, 

# option 3, separator is both at the start and the end
, a, b, c, d, 

Answer 1

没有标准方法，但是自然的方法是在结尾或开头（或结尾和开头）添加空字符串。使用一些更现代的语法：

>>> ', '.join(['', *['a', 'b', 'c', 'd']])
', a, b, c, d'
>>> ', '.join([*['a', 'b', 'c', 'd'], ''])
'a, b, c, d, '
>>> ', '.join(['', *['a', 'b', 'c', 'd'], ''])
', a, b, c, d, '

或者仅使用字符串格式：

>>> sep = ','
>>> data = ['a', 'b', 'c', 'd']
>>> f"{sep}{sep.join(data)}"
',a,b,c,d'
>>> f"{sep.join(data)}{sep}"
'a,b,c,d,'
>>> f"{sep}{sep.join(data)}{sep}"
',a,b,c,d,'

Answer 2

这是方法：

list1 = ['1','2','3','4']  

s = ","

r = f"{s}{s.join(list1)}"

p = f"{s.join(list1)}{s}"

q = f"{s}{s.join(list1)}{s}"


print(r)
print(p)
print(q)