act: a_run_method
al: 1
hash: хеш, полученный из страницы
method: messages.getConversations
param_count: 20
param_extended: 0
param_filter: all
param_offset: 0
param_v: 5.92

import requests,lxml.html,re,json
class invalid_password(Exception):
    def __init__(self, value):self.value = value
    def __str__(self):return repr(self.value)
class not_valid_method(Exception):
    def __init__(self, value):self.value = value
    def __str__(self):return repr(self.value)

class messages(object):
    def __init__(this,login,password):
        this.login = login
        this.password = password
        this.hashes = {}
        this.auth()
    def auth(this):
        headers = {'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36',
            'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
            'Accept-Language':'ru-ru,ru;q=0.8,en-us;q=0.5,en;q=0.3',
            'Accept-Encoding':'gzip, deflate',
            'Connection':'keep-alive',
            'DNT':'1'}
        this.session = requests.session()
        data = this.session.get('https://vk.com/', headers=headers)
        page = lxml.html.fromstring(data.content)
        form = page.forms[0]
        form.fields['email'] = this.login
        form.fields['pass'] = this.password
        response = this.session.post(form.action, data=form.form_values())
        if "onLoginDone" not in response.text: raise invalid_password("Неправильный пароль!")
        return
    def method(this,method,v=5.87,**params):
        if method not in this.hashes:
            this._get_hash(method)
        data = {'act': 'a_run_method','al': 1,
                'hash': this.hashes[method],
                'method': method,
                'param_v':v}
        for i in params:
            data["param_"+i] = params[i]
        answer = this.session.post('https://vk.com/dev',data=data)
        return json.loads(re.findall("<!>(\{.+)",answer.text)[-1])
    def _get_hash(this,method):
        html = this.session.get('https://vk.com/dev/'+method)
        hash_0 = re.findall('onclick="Dev.methodRun\(\'(.+?)\', this\);',html.text)
        if len(hash_0)==0:
            raise not_valid_method("method is not valid")
        this.hashes[method] = hash_0[0]