Execute these lines :

```
import numpy as np
import time

start = time.time()

t = []
for i in range(int(1e5)):
   t.append(i)

t = np.array(t)

end = time.time()
print(end-start)

```

And compare with these :

```
import numpy as np
import time

start = time.time()

t = np.array([])
for i in range(int(1e5)):
    t = np.append(t,[i])

end = time.time()
print(end-start)

```

The first is faster than the second by approximatively a factor 100 !

What is the reason ?