I was trying this
n = int(input())
m = int(input())
print(n,m)
for i in range(0,n):
for j in range(0,m):
ar[i][j] = int(input())
for i in range(0,n):
for j in range(0,m):
print (ar[i][j])
But it was showing an error
Traceback (most recent call last):
File "C:/Users/shivansh/Desktop/test.py", line 6, in <module>
ar[i][j] = int(input())
NameError: name 'ar' is not defined
I used to do the same in C language but it works. So, how to this in Python?
You haven't declared ar yet. In Python, you don't have to perform separate declaration and initialization; nevertheless, you can't perform operations on names willy-nilly.
Start off with something like this:
ar = [[0 for j in range(m)] for i in range(n)]
You should know that ar is not defined when you are trying to perform an assignment like ar[i][j] = int(input()), there are many ways to fix that.
In C/C++, I presume you would do such work like this:
#include <cstdio>
int main()
{
int m, n;
scanf("%d %d", &m, &n);
int **ar = new int*[m];
for(int i = 0; i < m; i++)
ar[i] = new int[n];
for(int i = 0; i < m; i++)
for(int j = 0; j < n; j++)
scanf("%d", &ar[i][j]);
// Do what you want to do
for(int i = 0; i < m; i++)
delete ar[i];
delete ar;
return 0;
}
Before you get inputs by scanf in C/C++, you should allocate storage by calling new or malloc, then you can perform your scanf, or it will crash.
It's very similar to what you had done in C/C++, according to your code, when you are trying to perform assignment to ar[i][j], Python has no idea what ar it is! So you have to let it know first.
A NOT-Pythonic way is do something like you did in C/C++:
n = int(input())
m = int(input())
ar = []
for i in range(m):
ar.append([])
for j in range(n):
k = int(input())
ar[i].append(k)
for i in range(m):
for j in range(n):
print(ar[i][j])
You initialize the list by ar = [] like you did int **ar = new int*[m]; in C/C++. For each row in the 2-d list, initialize the row by using ar.append([]) like you did ar[i] = new int[n]; in C/C++. Then, get your data by using input and append it to ar[i].
The way to perform such a job like above it's not very pythonic, instead, you can get it done by using a feature called List Comprehensions, then the code can be simplified into this:
n = int(input())
m = int(input())
ar = [[0 for j in range(n)] for i in range(m)]
for i in range(m):
for j in range(n):
k = int(input())
ar[i][j] = k
for i in range(m):
for j in range(n):
print(ar[i][j])
Note that the core ar = [[0 for j in range(n)] for i in range(m)] is a list comprehension that it creates a list which has m lists and for each list of these m lists it has n 0s.
You can initialize matrix in nested loop like this:
n = int(input()) # columns
m = int(input()) # rows
print(n,m)
matrix = []
for i in range(0,m):
matrix.append([])
for j in range(0,n):
matrix[i].append(0)
matrix[i][j] = int(input())
print matrix
Since you haven't declared ar before, you cannot assign elements at specific indexes. You can decalre a two dimensional list in this manner initialized to a certain value.
arr = [[value]*c for _ in range(r)]
where r and c are desired number of rows and columns respectively
Actually, you don't need the column count. Just enter the number of rows and give your input space separated.
rows = int(input('Enter rows\n'))
my_list = []
for i in range(rows):
my_list.append(list(map(int, input().split())))
At Python-3 we can easily take row and column input side by side as well as the data like a matrix by this process.
n, m = map(int, input("Enter row and column : ").split())
matrix = []
for i in range(0, n):
matrix.append(list(map(int, input().strip().split()))[:m])
also i found it helpful.
list=[]
n=int(input("enter no of rows"))
m=int(input("enter no of columns"))
for i in range(0,m):
list.append([])
for i in range(0,n):
for j in range(0,m):
list[i].append(j)
list[i][j]=0
for i in range(0,n):
for j in range(0,m):
print("entry in row:",i+1,"entry in column:",j+1)
list[i][j]=int(input())
print(list)
