pandas dataframe without column names

1Nope, you're not required to assign column names, nor do you need them to access any element.
2
3In [12]: df = pd.DataFrame([0])
4
5In [13]: df.ix[0,0]
6Out[13]: 0
7
8In [14]: df[0][0]
9Out[14]: 0
10In fact, you can think of the column already having a name -- it is the integer 0. Look at what happens when you provide a name
11
12In [15]: df    #Before naming the column
13Out[15]:
14   0
150  0
16
17In [16]: df.columns = ['ColA']
18In [17]: df    #Renamed
19Out[17]:
20   ColA
210     0
22
23In [18]: df['ColA'][0]    #Now you can access the column using the new name
24Out[18]: 0
25
26In [19]: df[0][0]         #... but trying the old name will not work
27---------------------------------------------------------------------------
28KeyError                                  Traceback (most recent call last)
29
30KeyError: 'no item named 0'
31You can still use DataFrame.ix just as before, though:
32
33In [20]: df.ix[0,0]
34Out[20]: 0