Question

我编写了一个网络抓取工具，它将货币兑换价值作为嵌套列表返回，我正在尝试编写一部分代码，通过此列表搜索给定名称并提取与之关联的货币值数据。

from urllib.request import urlopen
def find_element(line, s_pattern, e_pattern, position=0):
    shift = len(s_pattern)
    start = line.find(s_pattern, position) + shift
    position = start
    end = line.find(e_pattern, position)
    return (line[start:end], position)

def fetch(url):
    html = urlopen(url)
    records = []
    i = 0
    for line in html.readlines():
        line = line.decode()
        if "<tr><td>" not in line:
             continue  # skip if line don't contain rows
        if "Currency" in line:
             continue  # skip header

        start = "<tr><td>"
        end = "</td>"
        element, start_pos = find_element(line, start, end)
        records.append([element])
        start = "<td>"
        values = []
        for x in range(2):
            element, start_pos = find_element(line, start, end, start_pos)
            values.append(element)
        records[i].append(values)
        i = i + 1
    return(records)
def findCurrencyValue(records, currency_name):
    l = [[(records)]]
    d = dict(l)
    d[currency_name]
    return(d)
def main():
    url = "https://www.cs.purdue.edu/homes/jind/exchangerate.html"
    records = fetch(url)
    findCurrencyValue(records, "Argentine Peso")
    print(findCurrencyValue)
    print("currency exchange information is\n", records)
main()

但我收到了错误

ValueError: dictionary update sequence element #0 has length 1; 2 is required

Answer 1

在findCurrencyValue {}创建d = dict(l)，但l看起来像

[
  [
    [
      ['Argentine Peso', ['9.44195', '0.10591']],
      ['Australian Dollar', ['1.41824', '0.70510']],
      ['Bahraini Dinar', ['0.37743', '2.64953']],
      # etc
      ['Lithuanian Litas', ['3.07941', '0.32474']]
    ]
  ]
]

...即包含单个项目（列表）的列表。这不是dict()的有效输入。请改为d = dict(records)。

Answer 2

HTML永远不应该被解析。以下是相同的示例，但请求 + lxml （行数较少且准确）：

import requests
from lxml import html

URL = "https://www.cs.purdue.edu/homes/jind/exchangerate.html"

response = requests.get(URL)
tree = html.fromstring(response.content)

currency_dict = dict()

for row in tree.xpath('//table/tr')[1:]:
    currency, oneUSD, oneUnit = row.xpath('.//td/text()')
    currency_dict[currency] = dict(oneUSD=float(oneUSD), oneUnit=float(oneUnit))

search = "Argentine Peso" ## Change this value to the one you want to search for
oneUnit = currency_dict[search]['oneUnit']
oneUSD = currency_dict[search]['oneUSD']

print "Currency Exchange Rate for: {}".format(search)
print "1 USD = * Unit :  {}".format(oneUSD)
print "1 Unit = * USD :  {}".format(oneUnit)

输出：

Currency Exchange Rate for: Argentine Peso
1 USD = * Unit :  9.44195
1 Unit = * USD :  0.10591

替代 lxml （http://lxml.de/index.html#documentation） BeautifulSoup （http://www.crummy.com/software/BeautifulSoup/bs4/doc/）

我的代码中的列表/字典错误

2 个答案: