How do I know if my list has all 1s?

>>> x = [1, 1, 1, 1, 1, 1]
>>> all(el==1 for el in x)
True

This uses the function all with a generator expression.

If you always have only zeroes and ones in the list (or if you want to just check if the list doesn’t have any zeroes), then just use all without any additional tricks:

>>> x = [1, 0, 1, 1, 1, 0]
>>> all(x)
False

Benchmark of some solutions:
_{The numbers mean what time in milliseconds it took to run the solution once (average of 1000 timeit runs)}

Python 3.2.3

              all(el==1 for el in x): 0.0003 0.0008 0.7903 0.0804 0.0005 0.0006
                       x==[1]*len(x): 0.0002 0.0003 0.0714 0.0086 0.0045 0.0554
         not([1 for y in x if y!=1]): 0.0003 0.0005 0.4142 0.1117 0.1100 1.1630
                set(x).issubset({1}): 0.0003 0.0005 0.2039 0.0409 0.0476 0.5310
y = set(x); len(y)==1 and y.pop()==1:   WA   0.0006 0.2043 0.0517 0.0409 0.4170
                   max(x)==1==min(x):   RE   0.0006 0.4574 0.0460 0.0917 0.5466
                 tuple(set(x))==(1,):   WA   0.0006 0.2046 0.0410 0.0408 0.4238
not(bool(filter(lambda y: y!=1, x))):   WA     WA     WA   0.0004 0.0004 0.0004
                              all(x): 0.0001 0.0001 0.0839   WA   0.0001   WA  

Python 2.7.3

              all(el==1 for el in x): 0.0003 0.0008 0.7175 0.0751 0.0006 0.0006
                       x==[1]*len(x): 0.0002 0.0003 0.0741 0.0110 0.0094 0.1015
         not([1 for y in x if y!=1]): 0.0001 0.0003 0.3908 0.0948 0.0954 0.9840
                set(x).issubset({1}): 0.0003 0.0005 0.2084 0.0422 0.0420 0.4198
y = set(x); len(y)==1 and y.pop()==1:   WA   0.0006 0.2083 0.0421 0.0418 0.4178
                   max(x)==1==min(x):   RE   0.0006 0.4568 0.0442 0.0866 0.4937
                 tuple(set(x))==(1,):   WA   0.0006 0.2086 0.0424 0.0421 0.4202
not(bool(filter(lambda y: y!=1, x))): 0.0004 0.0011 0.9809 0.1936 0.1925 2.0007
                              all(x): 0.0001 0.0001 0.0811   WA   0.0001   WA  

[PyPy 1.9.0] Python 2.7.2

              all(el==1 for el in x): 0.0013 0.0093 0.4148 0.0508 0.0036 0.0038
                       x==[1]*len(x): 0.0006 0.0009 0.4557 0.0575 0.0177 0.1368
         not([1 for y in x if y!=1]): 0.0009 0.0015 175.10 7.0742 6.4390 714.15 # No, this wasn't run 1000 times. Had to time it separately.
                set(x).issubset({1}): 0.0010 0.0020 0.0657 0.0138 0.0139 0.1303
y = set(x); len(y)==1 and y.pop()==1:   WA   0.0011 0.0651 0.0137 0.0137 0.1296
                   max(x)==1==min(x):   RE   0.0011 0.5892 0.0615 0.1171 0.5994
                 tuple(set(x))==(1,):   WA   0.0014 0.0656 0.0163 0.0142 0.1302
not(bool(filter(lambda y: y!=1, x))): 0.0030 0.0081 0.2171 0.0689 0.0680 0.7599
                              all(x): 0.0011 0.0044 0.0230   WA   0.0013   WA  

The following test cases were used:

[] # True
[1]*6 # True
[1]*10000 # True
[1]*1000+[2]*1000 # False
[0]*1000+[1]*1000 # False
[random.randint(1, 2) for _ in range(20000)] # False

WA means that the solution gave a wrong answer; RE stands for runtime error.

So my verdict is, Winston Ewert‘s x==[1]*len(x) solution is the fastest in most cases. If you rarely have lists of all ones (the data is random, etc.) or you don’t want to use additional RAM, my solution works better. If the lists are small, the difference is negligible.