How to get a value from a cell of a dataframe?

I have constructed a condition that extract exactly one row from my data frame:

    d2 = df[(df['l_ext']==l_ext) & (df['item']==item) & (df['wn']==wn) & (df['wd']==1)]

Now I would like to take a value from a particular column:

    val = d2['col_name']

But as a result I get a data frame that contains one row and one column ( i.e. one cell). It is not what I need. I need one value (one float number). How can I do it in pandas?

If you have a DataFrame with only one row, then access the first (only) row as a Series using iloc, and then the value using the column name:

    In [3]: sub_df
              A         B
    2 -0.133653 -0.030854

    In [4]: sub_df.iloc[0]
    A   -0.133653
    B   -0.030854
    Name: 2, dtype: float64

    In [5]: sub_df.iloc[0]['A']
    Out[5]: -0.13365288513107493