语法练习：not_string

语法练习：not_string

题目：not_string

Given a string, return a new string where "not " has been added to the front. However, if the string already begins with “not”, return the string unchanged.

not_string(‘candy’) → ‘not candy’
not_string(‘x’) → ‘not x’
not_string(‘not bad’) → ‘not bad’

我的解答：

def not_string(str):
  if str[:3] == "not":
    return str
  else:
    return "not " + str
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Expected Run
not_string(‘candy’) → ‘not candy’ ‘not candy’ OK
not_string(‘x’) → ‘not x’ ‘not x’ OK
not_string(‘not bad’) → ‘not bad’ ‘not bad’ OK
not_string(‘bad’) → ‘not bad’ ‘not bad’ OK
not_string(‘not’) → ‘not’ ‘not’ OK
not_string(‘is not’) → ‘not is not’ ‘not is not’ OK
not_string(‘no’) → ‘not no’ ‘not no’ OK

All Correct

标答：

def not_string(str):
  if len(str) >= 3 and str[:3] == "not":
    return str
  return "not " + str
  # str[:3] goes from the start of the string up to but not
  # including index 3
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