think python学习心得-（5）迭代与字符串的使用

for while return break等语句，用法同C语言很像。

m=5.0
def sqr(a):
x=a
y=(x+m/x)/2
if abs(y-x)<0.00001:
print y
else:
sqr(y)

def sq(a):
x=a
y=(x+m/x)/2
flag= abs(y-x)
if flag < 0.00001:
return y
else:
sqr(y)
sq(m)

练习题7-3

import math
def sqr(a):
x=a
y=(x+m/x)/2
if abs(y-x)<0.00001:
print y
return y
else:
sqr(y)

def sq(a):
x=a
y=(x+m/x)/2
flag= abs(y-x)
if flag < 0.00001:
return y
else:
sqr(y)

for i in range(9):
j=float(i+1)
m=j
print j,math.sqrt(j),sq(j)

练习题7-4

import math
def eval_loop():
while True:
line = raw_input('>')
if line == 'done':
break
print eval(line)
eval_loop()
print 'Done!'
eval_loop()

练习题7-5

略。

8.字符串

练习8-1

word='fruit'
length=len(word)
for i in range(length):
print word[length-i-1]

练习8-2

prefixs='JKLMNP'
suffix = 'ack'

for letter in prefixs:
print letter+suffix

练习8-3

表示fruit中的全体字符

练习8-4

def find(word,letter,i):
index = i
while index < len(word):
if word[index]==letter:
return index
index = index+1
return -1
print find('Hellowordthisiszhangchangle!','s',2)

练习8-5

def count(word,letter):
count1 = 0
length = len(word)
for i in range (length):
if word[i] == letter:
count1=count1+1
return count1
print ('Please input a world and a letter to be counted')
word1=raw_input('>')
letter1=raw_input('>>')
print count(word1,letter1)

练习8-7

word='banana'
index=word.count('a')
print index

练习8-9