正则表达式来提取URL，而不使用不需要的单词

Question

目前我有如下字符串：

urls = [
    '<a href=https://energyplus.net/weather-download/asia_wmo_region_2/IND//IND_Kota.424520_ISHRAE/IND_Kota.424520_ISHRAE.epw>Download Weather File</a>',
    '<a href=https://energyplus.net/weather-download/europe_wmo_region_6/ESP//ESP_Alicante.083600_SWEC/ESP_Alicante.083600_SWEC.epw>Download Weather File</a>'
]

以及如下所示的正则表达式搜索：

for url in urls:
    match = re.search(r'href=[\'"]?([^\'" >]+)', url)
    if match:
        url = match.group(1)

url返回：

https://energyplus.net/weather-download/asia_wmo_region_2/IND//IND_Kota.424520_ISHRAE/IND_Kota.424520_ISHRAE.epw
https://energyplus.net/weather-download/europe_wmo_region_6/ESP//ESP_Alicante.083600_SWEC/ESP_Alicante.083600_SWEC.epw

我希望过滤掉包含单词SWEC的url，这样第二个url字符串就不匹配了。我认为这可能与(?!SWEC)有关，但即使这是正确的，我也不确定如何将其合并到当前的正则表达式搜索中

如果能得到建议，我将不胜感激

Answer 1

这里有一个使用"The Greatest Regex Trick Ever"的解决方案

for url in urls:
    match = re.search(r'href=[\'"]?(?:[^\'" >]*SWEC[^\'" >]*|([^\'" >]+))', url)
    if match and len(match.group(1)) > 0:
        url = match.group(1)

诀窍是先匹配你不想要的，然后捕获你想要的。这仍然会将URL与SWEC匹配，但捕获组将为空，因此您需要调整代码以处理此问题

Answer 2

您可以将.*添加到负前瞻(?!.*SWEC)，这样正则表达式将断言字符序列不匹配其后面紧跟单词SWEC的任何字符（换行符除外）。这种消极的前瞻不需要进入您的正则表达式捕获组，但它有助于减少查找有效匹配的步骤数

import re

urls = [
    '<a href=https://energyplus.net/weather-download/asia_wmo_region_2/IND//IND_Kota.424520_ISHRAE/IND_Kota.424520_ISHRAE.epw>Download Weather File</a>',
    '<a href=https://energyplus.net/weather-download/europe_wmo_region_6/ESP//ESP_Alicante.083600_SWEC/ESP_Alicante.083600_SWEC.epw>Download Weather File</a>'
]

for url in urls:
    match = re.search(r'href=[\'"]?((?!.*SWEC)[^\'" >]+)', url)
    if match:
        url = match.group(1)
        print(url)

# https://energyplus.net/weather-download/asia_wmo_region_2/IND//IND_Kota.424520_ISHRAE/IND_Kota.424520_ISHRAE.epw

Regex101example

Answer 3

这里可能不需要正则表达式。例如

试试看：

# list of urls
urls = [
    '<a href=https://energyplus.net/weather-download/asia_wmo_region_2/IND//IND_Kota.424520_ISHRAE/IND_Kota.424520_ISHRAE.epw>Download Weather File</a>',
    '<a href=https://energyplus.net/weather-download/europe_wmo_region_6/ESP//ESP_Alicante.083600_SWEC/ESP_Alicante.083600_SWEC.epw>Download Weather File</a>'
]

# check length of list (2)
print(len(urls))

# loop through the list
for i, url in enumerate(urls):
#for url in urls: #if you remove the printing you can revert to this and delete the above enumerate line
    #check if the substring 'SWEC' is in the current element of the list
    if 'SWEC' in url:
        #if so delete that element
        urls.remove(url)
        #print a message to say it's been deleted
        print('Found.  Removing item ' + str(i))

# recheck the length of the list (1)
print(len(urls))

甚至：

urls = [x for x in urls if 'SWEC' not in x]