python-3.x - 使用 BeautifulSoup 和 ftlib 访问 ftp 网站时出错

Question

我正在尝试访问网页以下载如下数据:

from bs4 import BeautifulSoup
import urllib.request
from lxml import html

download_url = "ftp://nomads.ncdc.noaa.gov/NARR_monthly/"

s = requests.session()                                                         


page = BeautifulSoup(s.get(download_url).text, "lxml")

但这会返回:

Traceback (most recent call last):

  File "<ipython-input-271-59c5b15a7e34>", line 1, in <module>
    r = requests.get(download_url)

  File "/anaconda3/lib/python3.6/site-packages/requests/api.py", line 72, in get
    return request('get', url, params=params, **kwargs)

  File "/anaconda3/lib/python3.6/site-packages/requests/api.py", line 58, in request
    return session.request(method=method, url=url, **kwargs)

  File "/anaconda3/lib/python3.6/site-packages/requests/sessions.py", line 508, in request
    resp = self.send(prep, **send_kwargs)

  File "/anaconda3/lib/python3.6/site-packages/requests/sessions.py", line 612, in send
    adapter = self.get_adapter(url=request.url)

  File "/anaconda3/lib/python3.6/site-packages/requests/sessions.py", line 703, in get_adapter
    raise InvalidSchema("No connection adapters were found for '%s'" % url)

InvalidSchema: No connection adapters were found for 'ftp://nomads.ncdc.noaa.gov/NARR_monthly/'

即使该网站正在运行。

通常，如果它有效，我会像这样循环遍历每个链接:

for a in page.find_all('a', href=True):
    file = a['href']
    print (file)

我也试过这个:

import ftplib

ftp = ftplib.FTP(download_url)

但这会返回:

  File "<ipython-input-284-60bd19e600fe>", line 1, in <module>
    ftp = ftplib.FTP(download_url)

  File "/anaconda3/lib/python3.6/ftplib.py", line 117, in __init__
    self.connect(host)

  File "/anaconda3/lib/python3.6/ftplib.py", line 152, in connect
    source_address=self.source_address)

  File "/anaconda3/lib/python3.6/socket.py", line 704, in create_connection
    for res in getaddrinfo(host, port, 0, SOCK_STREAM):

  File "/anaconda3/lib/python3.6/socket.py", line 745, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):

gaierror: [Errno 8] nodename nor servname provided, or not known

Answer 1

不幸的是 requests不支持 FTP 链接，但你可以使用内置的 urllib模块。

import urllib.request

download_url = "ftp://nomads.ncdc.noaa.gov/NARR_monthly/"
with urllib.request.urlopen(download_url) as r:
    data = r.read()

print(data)

响应不是 html，因此您无法使用 BeautifulSoup 解析它，但您可以使用正则表达式或字符串操作。

links = [
    download_url + line.split()[-1] 
    for line in data.decode().splitlines()
]
for link in links:
    print(link)

您也可以使用 ftplib如果您愿意，但您只能使用主机名。然后你可以 cd 到 'NARR_monthly' 并获取数据。

from ftplib import FTP

with FTP('nomads.ncdc.noaa.gov') as ftp:
    ftp.login() 
    ftp.cwd('NARR_monthly')
    data = ftp.nlst()

path = "ftp://nomads.ncdc.noaa.gov/NARR_monthly/"
links = [path + i for i in data]

有时主机会因为客户端太多而拒绝连接，因此您可能需要使用 try-except block 。