print two dimensional list

问题

I have a list, in which is another list and I want to doc.write(a)

a = [[1, 2, "hello"],
     [3, 5, "hi There"],
     [5,7,"I don't know"]]
doc.write(''.join(a))



TypeError: sequence item 0: expected str instance, list found

How can I handle this, do I have to make a for-loop in which I join and add all the sublists?

The real goal was to make it somehow readable for human beeing, but I didn't wanted a finished solution from you.

回答1:

You can try something like

>>> a = [[1, 2, "hello"],[3, 5, "hi There"],[5,7,"I don't know"]]
>>> 
>>> ''.join(str(r) for v in a for r in v)
"12hello35hi There57I don't know"

i.e.

doc.write(''.join(str(r) for v in a for r in v))

回答2:

There are different legal things you can do, and no way for anyone to say which one is right without knowing which one you want.

First, you can just write the str or repr of a:

>>> a=[[1, 2, "hello"],[3, 5, "hi There"],[5,7,"I don't know"]]
>>> repr(a)
'[[1, 2, \'hello\'], [3, 5, \'hi There\'], [5, 7, "I don\'t know"]]'

Note that this is what print does (it prints the str of whatever you give it—although with a list, the str is identical to the repr; they're both effectively '[' + ', '.join(map(repr, self)) + ']').

Second, you could use a format that's designed for data persistent, like JSON:

>>> json.dumps(a)
'[[1, 2, "hello"], [3, 5, "hi There"], [5, 7, "I don\'t know"]]'

Third, you can join together the repr of each element of a in some way of your choosing, which is trivial with a map or a comprehension. For example:

>>> '[' + ', '.join(map(repr, a)) + ']'
'[[1, 2, \'hello\'], [3, 5, \'hi There\'], [5, 7, "I don\'t know"]]'

… or …

>>> 'My stuff includes: ' + ','.join(map(repr, a)) + '\n'
'My stuff includes: [1, 2, \'hello\'],[3, 5, \'hi There\'],[5, 7, "I don\'t know"]\n'

Or you can do the same thing recursively.

Or you can flatten the list (e.g., flatten it one step with itertools.chain, or recursively with the recipes from the itertools docs or with the more-itertools package) and then stringify the pieces however you want and then join them up.

Or you can just write the word LIST.

All of those are perfectly valid things to pass to write.

回答3:

List comprehension would be the best choice:

>>> ''.join([str(item) for sublist in a for item in sublist])
"12hello35hi There57I don't know"

It's the most recommended approach in a similar SO question, considering performance and syntax.

回答4:

I was looking for an answer to this as well. After reading the comments here, this is what I came up with:

','.join(str(' '.join(str(x) for x in v)) for v in a)

This creates something like:

1 2 hello,3 5 hi There,5 7 I don't know

If you want all spaces as delimiters, then use ' ' instead of ',' at the front.

回答5:

What about using itertools?

from itertools import chain
doc.write(''.join(map(str, chain(a))))

Alternatively:

doc.write(''.join(str(i) for sub_list in a for i in sub_list))

You suggested a using a for loop. You could indeed do this, although the options above are probably better.

new_a = []
for sub_list in a:
    for i in sublist:
        new_a.append(str(i))
doc.write(''.join(new_a))

This is basically the previous option, but unrolled.

Unless you want to just write the first list, in which case you could do this:

doc.write(''.join(map(str, a[0])))

回答6:

It's difficult for me to be sure, because your question is too short, but it seems to me that you are in a XY problem, that is to say :
you ask a question about a Y problem that you think of as being the one that needs to be solved to goes out of an uphill X problem. But your real problem is that you think that the Y problem is the way to answer to the real problem X AND that you present here only the Y problem.
Writing that, I only paraphrase what is said here: XY problem

If I am right, my opinion is that you will have a better way to solve your real X problem using one of the following tools, that allow to serialize an object and to record the serialized object in a file:

pickle

marshal

shelve

I won't paraphrase and repeat all is the docs on these tools, read them.

If i am wrong and that you really just want to write an object under the form of a string representation, you can also do:

from pprint import pformat

a = [[1, 2, "hello"],
     [3, 5, "hi There"],
     [5,7,"I don't know"]]

with open('doc.txt','w') as f:
    f.write(pformat(a,width=12))

回答7:

You can also just use a simple list comprehension like this:

doc.write([x for x in i for i in a])

来源：https://stackoverflow.com/questions/19717769/print-two-dimensional-list

标签

python

python-3.x

python-3.3