How can take input of n number of lists in python?

Question

How can we take input of n number of lists in python

for example

2
1 2 3
4 5 6 7

here 2 is specifying number of lists that are going to input

1 2 3 is one list

4 5 6 7 is second list

another example

3 indicates 3 lists are going to input

1 2 3 is list one
4 5 6 8 is list two
2 3 5 7 id list three

i have done this code

n=input()
for i in range(n):
    b=map(int,raw_input().split())

i am struck with this how can i take input for n number of lists i able to take only one list into one variable i want take to different different variables

Please show your effort. What's the code you've come up with so far? — jbndlr
– jbndlr, Commented Nov 9, 2017 at 15:39
make an empty list before the loop and append each map to it instead of assigning them to a variable — Patrick Haugh
– Patrick Haugh, Commented Nov 9, 2017 at 15:45
The only real problem with your code so far is that b gets overwritten each time through the loop; you aren't accumulating your lists in a second, outer list yet. — chepner
– chepner, Commented Nov 9, 2017 at 15:45
i have edited my question and add my little code can you please check — saivinay manapuram
– saivinay manapuram, Commented Nov 9, 2017 at 15:45

tobias_k · Accepted Answer · 2017-11-09 15:58:44Z

1

i want take to different different variables

You can not assign the input to "different" variables in the loop, particularly if you do not know how large n will be. Instead, you should append the different values of b to a list of lists, e.g. bs.

n = input()
bs = []
for i in range(n):
    bs.append(map(int, raw_input().split()))

Or use a list comprehension:

bs = [map(int, raw_input().split()) for _ in range(n)]

edited Nov 9, 2017 at 15:58

answered Nov 9, 2017 at 15:55

tobias_k

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2 Comments

saivinay manapuram Over a year ago

instead of append all list to one list can't we take to different different variables

tobias_k Over a year ago

@saivinaymanapuram No, you can't, and there is really no good reason you would want to. This looks like some sort of programming excercise (Hackerrank, maybe?), and you will probably want to do the same operation for each of those lists. So putting them in a list is much better than having many differently named variables.

pydvlpr · Accepted Answer · 2017-11-09 16:03:59Z

0

do you want to read from file or cli?

If you read from file, you can iterate over its content line by line and work only in the specific lines.

The lines input you can split to get the single numbers into a list.

nums=[]
with open(infile.txt) as f:

 n=0
 for i, line in enumerate(f):
     if i==1:
          n == 1
     elif i <= n
         nums[i] = line.split()

answered Nov 9, 2017 at 16:03

pydvlpr

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Comments

Prateek Sanyal · Accepted Answer · 2017-11-09 16:43:28Z

0

There are a few things to fix:

You need to convert your input 'n' to an integer.
Your 'b' gets overwritten with every iteration of the loop.
Why are you using 'raw_input' in the second case? 'input' will give you a sanitized version of the input which is preferable in this case (so that a malicious user cannot inject code).

Keep it simple and use lists instead of a map.


n = int(input())
rows = [] # will contain the input as a list of integers
for i in range(n):
    row_string = input()
    row = [int(num) for num in row_string.split()]
    rows.append(row)

edited Nov 9, 2017 at 16:43

answered Nov 9, 2017 at 16:07

Prateek Sanyal

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2 Comments

tobias_k Over a year ago

It seems like you are confusing what input and raw_input do. raw_input only exists in Python 2 (thus that's what OP seems to use), where it does the same thing as input in Python 3, whereas input in Python 2also evaluates the input, thus no cast to int needed.

Prateek Sanyal Over a year ago

@tobias_k thanks for the feedback. I am aware of this but isn't it usually an unsafe practice to literally evaluate input? If the code snippet is the full extent of the usage then maybe there is no risk but what about if this snippet was used in a bigger software? Is the risk of injection worth it?

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