# Python | Print diagonals of 2D list

Given a 2D list (with equal length of sublists), write a Python program to print both the diagonals of the given 2D list.

Examples:

```Input : [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Output : Diagnol 1 - [1, 5, 9]
Diagnol 2 - [3, 5, 7]

Input : [['a', 'b'], ['c', 'd']]
Output : Diagnol 1 - ['a', 'd']
Diagnol 2 - ['b', 'c']

```

Approach #1 : Using Python `xrange()`

We can use one-liner list comprehension along with `xrange()` function. xrange() is used to iterate a certain number of times in for loops. Thus, we print the element at `[i][i]` position in every iteration of loop. [Works in Python2]

 `# Python2 program to print diagonals in 2D list ` ` `  `def` `printDiagnol(lst): ` `    ``# To print Primary Diagnol ` `    ``print``(``'Diagnol 1 -'``), ` `    ``print``([lst[i][i] ``for` `i ``in` `xrange``(``len``(lst))]) ` ` `  `    ``# To print Secondry Diagnol ` `    ``print``(``'Diagnol 2 -'``), ` `    ``print``([lst[i][``len``(lst)``-``1``-``i] ``for` `i ``in` `xrange``(``len``(lst))]) ` ` `  `     `  `# Driver code ` `lst ``=` `[[``1``, ``2``, ``3``], ` `       ``[``4``, ``5``, ``6``],  ` `       ``[``7``, ``8``, ``9``]] ` ` `  `printDiagnol(lst) `

Output:

```Diagnol 1 - [1, 5, 9]
Diagnol 2 - [3, 5, 7]
```

Approach #2 : Using `range()`

This method is similar to Approach #1. The advantage of `range()` is that it works for both the versions of Python i.e. Python2 and Python3.

 `# Python3 program to print diagonals in 2D list ` ` `  `def` `printDiagnol(lst): ` ` `  `    ``# To print Primary Diagnol ` `    ``print``(``'Diagnol 1 - '``, end ``=``"") ` `    ``print``([lst[i][i] ``for` `i ``in` `range``(``len``(lst))]) ` `     `  `    ``# To print Secondry Diagnol ` `    ``print``(``'Diagnol 2 - '``, end ``=``"") ` `    ``print``([lst[i][``len``(lst)``-``i``-``1``] ``for` `i ``in` `range``(``len``(lst))]) ` `     `  `# Driver code ` `lst ``=` `[[``1``, ``2``, ``3``], [``4``, ``5``, ``6``], [``7``, ``8``, ``9``]] ` `printDiagnol(lst) `

Output:

```Diagnol 1 - [1, 5, 9]
Diagnol 2 - [3, 5, 7]
```

Approach #3 : Using `enumerate()`

Python enumerate() is also an alternative to above mentioned methods. It uses two variable ‘i’ and ‘r’ two traverse through enumerate(lst) and simply return the ith element of ‘r’.

 `# Python3 program to print diagonals in 2D list ` ` `  `def` `printDiagnol(lst): ` `    ``# To print Primary Diagnol ` `    ``print``(``'Diagnol 1 - '``, end ``=``"") ` `    ``print``([r[i] ``for` `i, r ``in` `enumerate``(lst)]) ` `     `  `    ``# To print Secondary Diagnol ` `    ``print``(``'Diagnol 2 - '``, end ``=``"") ` `    ``print``([r[~i] ``for` `i, r ``in` `enumerate``(lst)]) ` ` `  `     `  `# Driver code ` `lst ``=` `[[``1``, ``2``, ``3``], [``4``, ``5``, ``6``], [``7``, ``8``, ``9``]] ` `printDiagnol(lst) `

Output:

```Diagnol 1 - [1, 5, 9]
Diagnol 2 - [3, 5, 7]
```

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