通过Python3从网页读取文本文件

Question

import re
import urllib
hand=urllib.request.urlopen("http://www.pythonlearn.com/code/mbox-short.txt")
qq=hand.read().decode('utf-8') 
numlist=[]
for line in qq:
    line.rstrip()
    stuff=re.findall("^X-DSPAM-Confidence: ([0-9.]+)",line)
    if len(stuff)!=1:
        continue
    num=float(stuff[0])
    numlist.append(num)
print('Maximum:',max(numlist))

The variable qq contains all the strings from the text file. However, the for loop doesn't work and numlist is still empty.

When I download the text file as a local file then read it, everything is ok.

Answer 1

Use the regex on qq using the multiline flag re.M , you are iterating over a string so going character by character , not line by line so you are calling findall on single characters:

In [18]: re.findall("^X-DSPAM-Confidence: ([0-9.]+)",qq, re.M)
Out [18]: ['0.8475', '0.6178', '0.6961', '0.7565', '0.7626', '0.7556', '0.7002', '0.7615', '0.7601', '0.7605', '0.6959', '0.7606', '0.7559', '0.7605', '0.6932', '0.7558', '0.6526', '0.6948', '0.6528', '0.7002', '0.7554', '0.6956', '0.6959', '0.7556', '0.9846', '0.8509', '0.9907']

What you are doing is equivalnet to:

In [13]: s = "foo\nbar"

In [14]: for c in s:
   ....:    stuff=re.findall("^X-DSPAM-Confidence: ([0-9.]+)",c)
            print(c)
   ....:     
f
o
o


b
a
r

If you want floats, you can cast with map :

list(map(float,re.findall("^X-DSPAM-Confidence: ([0-9.]+)",qq, re.M)))

But if you just want the max, you can pass a key to max :

In [22]: max(re.findall("^X-DSPAM-Confidence: ([0-9.]+)",qq, re.M),key=float)
Out[22]: '0.9907'

So all you need is three lines:

In [28]: hand=urllib.request.urlopen("http://www.pythonlearn.com/code/mbox-short.txt")

In [29]: qq = hand.read().decode('utf-8')

In [30]: max(re.findall("^X-DSPAM-Confidence: ([0-9.]+)",qq, re.M),key=float)
Out[30]: '0.9907'

If you wanted to go line by line, iterate directly over hand :

import re
import urllib

hand = urllib.request.urlopen("http://www.pythonlearn.com/code/mbox-short.txt")
numlist = []
# iterate over each line like a file object
for line in hand:
    stuff = re.search("^X-DSPAM-Confidence: ([0-9.]+)", line.decode("utf-8"))
    if stuff:
        numlist.append(float(stuff.group(1)))
print('Maximum:', max(numlist))