爬蟲練習（一）：模擬登錄並爬取表格數據（提交表單數據）

內容有：

• 通過requests庫模擬表單提交
• 通過pandas庫提取網頁表格

目標分析

網址是這個：https://www.ctic.org/crm?tdsourcetag=s_pctim_aiomsg

打開長這樣：

點擊View Summary後出現目標網頁長這樣

目標數據所在網頁的網址是這樣的：https://www.ctic.org/crm/?action=result，剛剛選擇的那些參數並沒有作爲url的參數啊！網址網頁都變了，所以也不是ajax

嘗試獲取目標頁面

讓我來點擊View Summary這個按鈕時到底發生了啥：右鍵View Summary檢查是這樣：

提交的爲 post請求：
點擊View Summary，到DevTools裏找network第一條：

不管三七二十一，post一下試試看

import requests

url = 'https://www.ctic.org/crm?tdsourcetag=s_pctim_aiomsg'
headers = {'user-agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) '
           'AppleWebKit/537.36 (KHTML, like Gecko) '
           'Chrome/74.0.3729.131 Safari/537.36',
           'Host': 'www.ctic.org'}
data = {'_csrf': 'SjFKLWxVVkkaSRBYQWYYCA1TMG8iYR8ReUYcSj04Jh4EBzIdBGwmLw==',
        'CRMSearchForm[year]': '2011',
        'CRMSearchForm[format]': 'Acres',
        'CRMSearchForm[area]': 'County',
        'CRMSearchForm[region]': 'Midwest',
        'CRMSearchForm[state]': 'IL',
        'CRMSearchForm[county]': 'Adams',
        'CRMSearchForm[crop_type]': 'All',
        'summary': 'county'}
response = requests.post(url, data=data, headers=headers)
print(response.status_code)

果不其然，輸出400……

嘗試用cookies

首先，搞不清cookies具體是啥，只知道它是用來維持會話的，應該來自於第一次get，搞出來看看先：

response1 = requests.get(url, headers=headers)
if response1.status_code == 200:
    cookies = response1.cookies
    print(cookies)

輸出：

<RequestsCookieJar[<Cookie PHPSESSID=52asgghnqsntitqd7c8dqesgh6 for www.ctic.org/>, <Cookie _csrf=2571c72a4ca9699915ea4037b967827150715252de98ea2173b162fa376bad33s%3A32%3A%22TAhjwgNo5ElZzV55k3DMeFoc5TWrEmXj%22%3B for www.ctic.org/>]>

直接把它放到post裏試試

response2 = requests.post(url, data=data, headers=headers, cookies=cookies)
print(response2.status_code)

還是400，

post請求所帶的data中那個一開始就顯得很可疑的_csrf

那個完全看不懂的cookies裏好像就有一個_csrf啊！但是兩個_csrf的值很明顯結構不一樣，試了一下把data裏的_csrf換成cookies裏的_csrf確實也不行。

這個兩個_csrf雖然不相等，但是應該是匹配的，剛剛的data來自瀏覽器，cookies來自python程序，所以不匹配！
點開瀏覽器的DevTools，Ctrl+F搜索了一下，嘿嘿，發現了：

這三處。

第一處那裏的下一行的csrf_token很明顯就是post請求所帶的data裏的_csrf，另外兩個是js裏的函數，雖然js沒好好學但也能看出來這倆是通過post請求獲得州名和縣名的，Binggo！一下子解決兩個問題。

爲了驗證猜想，打算先直接用requests獲取點擊View Summary前的頁面的HTML和cookies，將從HTML中提取的csrf_token值作爲點擊View Summary時post請求的data裏的_csrf值，同時附上cookies，這樣兩處_csrf就應該是匹配的了：

from lxml import etree
response1 = requests.get(url, headers=headers)
cookies = response1.cookies
html = etree.HTML(response1.text)
csrf_token = html.xpath('/html/head/meta[3]/@content')[0]
data.update({'_csrf': csrf_token})
response2 = requests.post(url, data=data, headers=headers, cookies=cookies)
print(response2.status_code)

輸出200，雖然和Chrome顯示的302不一樣，但是也表示成功

嘗試pandas庫提取網頁表格

現在既然已經拿到了目標頁面的HTML，那在獲取所有年、地區、州名、縣名之前，先測試一下pandas.read_html提取網頁表格的功能。

import pandas as pd
df = pd.read_html(response2.text)[0]
print(df)

準備所有參數

接下來要獲取所有年、地區、州名、縣名。年份和地區是寫死在HTML裏的，直接xpath獲取：

州名、縣名根據之前發現的兩個js函數，要用post請求來獲得，其中州名要根據地區名獲取，縣名要根據州名獲取，套兩層循環就行

def new():
    session = requests.Session()
    response = session.get(url=url, headers=headers)
    html = etree.HTML(response.text)
    return session, html

session, html = new()
years = html.xpath('//*[@id="crmsearchform-year"]/option/text()')
regions = html.xpath('//*[@id="crmsearchform-region"]/option/text()')
_csrf = html.xpath('/html/head/meta[3]/@content')[0]
region_state = {}
state_county = {}
for region in regions:
    data = {'region': region, '_csrf': _csrf}
    response = session.post(url_state, data=data)
    html = etree.HTML(response.json())
    region_state[region] = {x: y for x, y in
                            zip(html.xpath('//option/@value'),
                                html.xpath('//option/text()'))}
    for state in region_state[region]:
        data = {'state': state, '_csrf': _csrf}
        response = session.post(url_county, data=data)
        html = etree.HTML(response.json())
        state_county[state] = html.xpath('//option/@value')

使用requests.Session就完全不需要自己管理cookies了，方便！
然後把所有年、地區、州名、縣名的可能組合先整理成csv文件，一會直接從csv裏讀取並構造post請求的data字典：

remain = [[str(year), str(region), str(state), str(county)] 
         for year in years for region in regions
         for state in region_state[region] for county in state_county[state]]
remain = pd.DataFrame(remain, columns=['CRMSearchForm[year]',
                                       'CRMSearchForm[region]',
                                       'CRMSearchForm[state]',
                                       'CRMSearchForm[county]'])
remain.to_csv('remain.csv', index=False)
# 由於州名有縮寫和全稱，也本地保存一份
import json
with open('region_state.json', 'w') as json_file:
        json.dump(region_state, json_file, indent=4)

正式開始

import pyodbc
with open("region_state.json") as json_file:
    region_state = json.load(json_file)
data = pd.read_csv('remain.csv')
# 讀取已經爬取的
cnxn = pyodbc.connect('DRIVER={Microsoft Access Driver (*.mdb, *.accdb)};'
                      'DBQ=./ctic_crm.accdb')
crsr = cnxn.cursor()
crsr.execute('select Year_, Region, State, County from ctic_crm')
done = crsr.fetchall()
done = [list(x) for x in done]
done = pd.DataFrame([list(x) for x in done], columns=['CRMSearchForm[year]',
                                                      'CRMSearchForm[region]',
                                                      'CRMSearchForm[state]',
                                                      'CRMSearchForm[county]'])
done['CRMSearchForm[year]'] = done['CRMSearchForm[year]'].astype('int64')
state2st = {y: x for z in region_state.values() for x, y in z.items()}
done['CRMSearchForm[state]'] = [state2st[x]
                                for x in done['CRMSearchForm[state]']]
# 排除已經爬取的
remain = data.append(done)
remain = remain.drop_duplicates(keep=False)
total = len(remain)
print(f'{total} left.n')
del data

# %%
remain['CRMSearchForm[year]'] = remain['CRMSearchForm[year]'].astype('str')
columns = ['Crop',
           'Total_Planted_Acres',
           'Conservation_Tillage_No_Till',
           'Conservation_Tillage_Ridge_Till',
           'Conservation_Tillage_Mulch_Till',
           'Conservation_Tillage_Total',
           'Other_Tillage_Practices_Reduced_Till15_30_Residue',
           'Other_Tillage_Practices_Conventional_Till0_15_Residue']
fields = ['Year_', 'Units', 'Area', 'Region', 'State', 'County'] + columns
data = {'CRMSearchForm[format]': 'Acres',
        'CRMSearchForm[area]': 'County',
        'CRMSearchForm[crop_type]': 'All',
        'summary': 'county'}
headers = {'user-agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) '
           'AppleWebKit/537.36 (KHTML, like Gecko) '
           'Chrome/74.0.3729.131 Safari/537.36',
           'Host': 'www.ctic.org',
           'Upgrade-Insecure-Requests': '1',
           'DNT': '1',
           'Connection': 'keep-alive'}
url = 'https://www.ctic.org/crm?tdsourcetag=s_pctim_aiomsg'
headers2 = headers.copy()
headers2 = headers2.update({'Referer': url,
                            'Origin': 'https://www.ctic.org'})
def new():
    session = requests.Session()
    response = session.get(url=url, headers=headers)
    html = etree.HTML(response.text)
    _csrf = html.xpath('/html/head/meta[3]/@content')[0]
    return session, _csrf
session, _csrf = new()
for _, row in remain.iterrows():
    temp = dict(row)
    data.update(temp)
    data.update({'_csrf': _csrf})
    while True:
        try:
            response = session.post(url, data=data, headers=headers2, timeout=15)
            break
        except Exception as e:
            session.close()
            print(e)
            print('nSleep 30s.n')
            time.sleep(30)
            session, _csrf = new()
            data.update({'_csrf': _csrf})

    df = pd.read_html(response.text)[0].dropna(how='all')
    df.columns = columns
    df['Year_'] = int(temp['CRMSearchForm[year]'])
    df['Units'] = 'Acres'
    df['Area'] = 'County'
    df['Region'] = temp['CRMSearchForm[region]']
    df['State'] = region_state[temp['CRMSearchForm[region]']][temp['CRMSearchForm[state]']]
    df['County'] = temp['CRMSearchForm[county]']
    df = df.reindex(columns=fields)
    for record in df.itertuples(index=False):
        tuple_record = tuple(record)
        sql_insert = f'INSERT INTO ctic_crm VALUES {tuple_record}'
        sql_insert = sql_insert.replace(', nan,', ', null,')
        crsr.execute(sql_insert)
        crsr.commit()
    print(total, row.to_list())
    total -= 1
else:
    print('Done!')
    crsr.close()
    cnxn.close()