如何通过遍历整数和字符串的组合来创建变量？

Question

So I want to create variables by looping through some sort of name assigning statement or function. I want to end up having variables titled " t1 , t2 , t3 " etc. How can I accomplish what

i = 1
while 1:
    ("t" + str(i)) = [0,0,0,0]
    i = i + 1

looks like it would do. (Keep the str("t") at the front than make the second character the changing int(i) . This is to create variables to later put in an array without having to type them out in the the code.) I'm trying to make a list of 10,000 lists with 4 elements each. Is this more clear?

Answer 1

Don't try.

Instead, use a single dictionary to keep all the values - your titles can be the keys:

my_dict = {}
for i in range(1, 4):
    my_dict['t%s' % i] = foo

Answer 2

While it is technically possible to do what you want, it's a really bad practice. This is exactly the use case that lists (or arrays) were made for, and you should be using one here.

Based on your code sample, something like

t = [[0] * 4 for i in xrange(10000)]

(as David Alber mentioned in a comment) should work for you; it will create a list of 10000 lists of 4 elements each.

PS In Python 3, the xrange function has been renamed to range .

Answer 3

t = [[0] * 4] * 10000 works, but probably doesn't do what you expect. Rather than creating a list of 10000 lists, it will create a list of 10000 references to a single list. Have a look at what happens when you try to start changing elements of the inner lists:

>>> t = [[0] * 4] * 3
>>> t
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>> t[0][0] = 1
>>> t
[[1, 0, 0, 0], [1, 0, 0, 0], [1, 0, 0, 0]]

Instead, the following is probably what you were expecting:

>>> t = [[0] * 4 for _ in xrange(3)]
>>> t
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>> t[0][0] = 1
>>> t
[[1, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]

The reason is that multiplying a list just creates a longer list with multiple references to the elements inside the original list. This is almost never a good idea unless you know the list contains entirely immutable objects (such as numbers and strings); that's why it's still okay to use list multiplication in [0] * 4 in my version of the answer, even though the outer list multiplication in [[0] * 4] * 10000 is dangerous.