python loops_python - loops

loops and iteration

While

while loops are called indefinite loops because they keep going until a logical condition becomes False.

# break out of a loop

while True:

line = input('>')

if line == 'done':

break

print(line)

print('done!')

# finishing an iteration with contine

while True:

line = input('>')

if line[0] == '#':

continue # go up back to the tope of loop

if line == 'done':

break # get out of the loop

print(line)

print('done!')

for

definite loops iterate through the members of a set.

for i in [5,4,3,2,1]: # i is iteration variable

print(i)

print('blast off!')

friends = ['ke','xinlei','xjc']

for friend in friends:

print('hi',friend)

print('ok')

# count

count = 0

sum = 0

print('before',count,sum)

for things in [9,41,12,3,74,15]:

count += 1

sum += things

print(things,count,sum)

print('after',count,sum)

# a none type

smallest = None

print('before',smallest)

for value in [9,41,12,3,74,15]:

if smallest is None:

smallest = value

elif value < smallest:

smallest = value

print(smallest,value)

print('after',smallest)

# 'is' is stronger than '==' e.g. 0 == 0.00

# use is for None/ Ture False, not recommended use for integer

condition

astr = 'hello'

try:

print('hello')

astr = int(astr) #注意此处错误

except: # 只在try错误的时候触发 每一条

astr = -1

print('First', istr)