001、

>>> import re
>>> str = "sefderfhjuynb"
>>> re.findall(".{3}", str)                  ## 步长为3
['sef', 'der', 'fhj', 'uyn']
>>> re.findall(".{2}", str)                  ## 步长为2
['se', 'fd', 'er', 'fh', 'ju', 'yn']

不能整除？：

>>> str
'sefderfhjuynb'
>>> remainder = len(str) % 3
>>> remainder
1
>>> result = re.findall(".{3}", str)
>>> result
['sef', 'der', 'fhj', 'uyn']
>>> result.extend(list(str[-remainder:]))
>>> result
['sef', 'der', 'fhj', 'uyn', 'b']

002、

(base) [email protected]:/home/test2# ls
test.py
(base) [email protected]:/home/test2# cat test.py      ## 测试程序
#!/usr/bin/python
str = 'sefderfhjuynb'

steps = len(str) // 3
remainder = len(str) % 3

start = 0
end = 3
result = []
for i in range(steps):
    result.append(str[start:end])
    start += 3
    end += 3

if remainder != 0:
    result.append(str[-remainder:])

print(result)
(base) [email protected]:/home/test2# python test.py   ## 运行结果
['sef', 'der', 'fhj', 'uyn', 'b']