Python快速入门（2）练习题

# C. fix_start
# Given a string s, return a string
# where all occurences of its first char have
# been changed to '*', except do not change
# the first char itself.
# e.g. 'babble' yields 'ba**le'
# Assume that the string is length 1 or more.
# Hint: s.replace(stra, strb) returns a version of string s
# where all instances of stra have been replaced by strb.

def fix_start(s):  # +++your code here+++  # LAB(begin solution)  front = s[0]  back = s[1:]  fixed_back = back.replace(front, '*')  return front + fixed_back

# E. not_bad
# Given a string, find the first appearance of the
# substring 'not' and 'bad'. If the 'bad' follows
# the 'not', replace the whole 'not'...'bad' substring
# with 'good'.
# Return the resulting string.
# So 'This dinner is not that bad!' yields:
# This dinner is good!

def not_bad(s):  # +++your code here+++  # LAB(begin solution)  n = s.find('not')  b = s.find('bad')  if n != -1 and b != -1 and b > n:s = s[:n] + 'good' + s[b+3:]  return s