python for循环字符串,Python在嵌套的for循环中遍历字符串

I'm just wondering, I'm trying to make a very simple text processing or reduction. I want to replace all spaces (without these in " ") by one. I also have some semantic action dependent on each character read, so I that's why I don't want to use any regex. It's some kind of pseudo FSM model.

So here's the the deal:

s = '''that's my string, " keep these spaces " but reduce these '''

Desired ouput:

that's my string, " keep these spaces " but reduce these

What I would like to do is something like this: (I don't mention the '"' case to keep the example simple)

out = ""

for i in range(len(s)):

if s[i].isspace():

out += ' '

while s[i].isspace():

i += 1

else:

out += s[i]

I don't quite understand how the scopes are created or shared in this case.

Thank you for advice.

解决方案

I also have some semantic action dependent on each character read ... It's some kind of pseudo FSM model.

You could actually implement an FSM:

s = '''that's my string, " keep these spaces " but reduce these '''

normal, quoted, eating = 0,1,2

state = eating

result = ''

for ch in s:

if (state, ch) == (eating, ' '):

continue

elif (state,ch) == (eating, '"'):

result += ch

state = quoted

elif state == eating:

result += ch

state = normal

elif (state, ch) == (quoted, '"'):

result += ch

state = normal

elif state == quoted:

result += ch

elif (state,ch) == (normal, '"'):

result += ch

state = quoted

elif (state,ch) == (normal, ' '):

result += ch

state = eating

else: # state == normal

result += ch

print result

Or, the data-driven version:

actions = {

'normal' : {

' ' : lambda x: ('eating', ' '),

'"' : lambda x: ('quoted', '"'),

None: lambda x: ('normal', x)

},

'eating' : {

' ' : lambda x: ('eating', ''),

'"' : lambda x: ('quoted', '"'),

None: lambda x: ('normal', x)

},

'quoted' : {

'"' : lambda x: ('normal', '"'),

'\': lambda x: ('escaped', '\'),

None: lambda x: ('quoted', x)

},

'escaped' : {

None: lambda x: ('quoted', x)

}

}

def reduce(s):

result = ''

state = 'eating'

for ch in s:

state, ch = actions[state].get(ch, actions[state][None])(ch)

result += ch

return result

s = '''that's my string, " keep these spaces " but reduce these '''

print reduce(s)