```python
import time
import dis
```


```python
%%timeit
a = list(range(2**20))
```

    10 loops, best of 3: 25.5 ms per loop



```python
%%timeit
a = list(i for i in range(2**20))
```

    10 loops, best of 3: 60.1 ms per loop



```python
%%timeit
a = [i for i in range(2**20)]
```

    10 loops, best of 3: 39.3 ms per loop



```python
%%timeit
a = []
for i in range(2**20):
    a.append(i)
```

    10 loops, best of 3: 76.6 ms per loop



```python
pairs = [(i,i) for i in range(2**20)]
ints = list(range(2**20))
```


```python
%%timeit
a = dict(pairs)
```

    10 loops, best of 3: 50.1 ms per loop



```python
%%timeit
a = dict((i,i) for i in ints)
```

    10 loops, best of 3: 95.9 ms per loop



```python
%%timeit
a = {i for i in pairs}
```

    1 loop, best of 3: 213 ms per loop



```python
%%timeit
a = {i: i for i in ints}
```

    10 loops, best of 3: 59.5 ms per loop



```python
%%timeit
a = {i: j for i, j in enumerate(ints)}
```

    10 loops, best of 3: 87.1 ms per loop



```python
dis.dis(compile('list(range(2**20))', '<stdin>', 'exec'))
```

      1           0 LOAD_NAME                0 (list)
                  3 LOAD_NAME                1 (range)
                  6 LOAD_CONST               3 (1048576)
                  9 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
                 12 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
                 15 POP_TOP
                 16 LOAD_CONST               2 (None)
                 19 RETURN_VALUE



```python
dis.dis(compile('[i for i in range(2**20)]', '<stdin>', 'exec'))
```

      1           0 LOAD_CONST               0 (<code object <listcomp> at 0x7fe20c574d20, file "<stdin>", line 1>)
                  3 LOAD_CONST               1 ('<listcomp>')
                  6 MAKE_FUNCTION            0
                  9 LOAD_NAME                0 (range)
                 12 LOAD_CONST               5 (1048576)
                 15 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
                 18 GET_ITER
                 19 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
                 22 POP_TOP
                 23 LOAD_CONST               4 (None)
                 26 RETURN_VALUE



```python

```