get data from xml using pandas

I'm trying to get some data from xml using pandas. Currently I have "working" code, and by working i mean it almost work.

import pandas as pd
import requests
from bs4 import BeautifulSoup

url = "http://ift.tt/2g7RwGi?"


response = requests.get(url).content
soup = BeautifulSoup(response)

tables = soup.find_all('tabela_rozklad')

tags = ['dzien', 'godz', 'ilosc', 'tyg', 'id_naucz', 'id_sala',
'id_prz', 'rodz', 'grupa', 'id_st', 'sem', 'id_spec']

df = pd.DataFrame()
for table in tables:
    all = map(lambda x: table.find(x).text, tags)
    df = df.append([all])

df.columns = tags

a = df[(df.sem == "1")]
a = a[(a.id_spec == "0")]
a = a[(a.dzien == "1")]
print(a)

So I'm getting error on "a = df[(df.sem == "1")]" which is :

File "pandas\index.pyx", line 139, in pandas.index.IndexEngine.get_loc (pandas\index.c:4443)

File "pandas\index.pyx", line 161, in pandas.index.IndexEngine.get_loc (pandas\index.c:4289)

File "pandas\src\hashtable_class_helper.pxi", line 732, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:13733)

File "pandas\src\hashtable_class_helper.pxi", line 740, in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:13687)

As i read other stacks questions I saw people suggest using df.loc so i modyfied this line into

a = df.loc[(df.sem == "1")]

Now code compile but the results show like this line doesn't exists. Need to mention that the problem is with the "sem" tag only. Rest works perfectly but unfortunately i need to use exactly this tag. If anyone could explain what i causing this error and how to fix it I would be grateful.