Add comprehensions and grid example

Author: Sahil

day3/comprehensions.py

@@ -0,0 +1,18 @@
+# given a list of strings, find lengths of each of them
+names = ["scaler", "interviewbit"]
+len_list = []
+for name in names:
+  len_list.append(len(name))
+print(len_list)
+
+# using list comprehension
+len_list = [len(name) for name in names]
+len_list = [("length", len(name)) for name in names]
+print(len_list)
+# with odd lengths
+len_list = [("length", len(name)) for name in names if len(name) % 2 == 1]
+print(len_list)
+
+# sum of all even numbers from 1 to 100
+sum_even = sum([num for num in range(1, 101) if num % 2 == 0])
+print(sum_even)

day3/grid_city.py

@@ -0,0 +1,12 @@
+# take a m * n grid (matrix) as input
+# print the sum of all the elements, max,
+# and the sum of left_diagonal
+
+n, m = map(int, input().split())
+
+matrix = []
+for r in range(n):
+  row = list(map(int, input().split()))
+  matrix.append(row)
+
+print(matrix)

lecture3.md

@@ -509,4 +509,31 @@ print(day_mapping.keys())
 
 ## Mutability Summary
 - Basic Types: `int`, `float`, `decimal`, `str`, `bool` all are immutable
-- Container Types: `list`, `set` and `dict` are mutable while `tuple` is not
+- Container Types: `list`, `set` and `dict` are mutable while `tuple` is not
+
+## List Comprehensions
+
+```py
+# given a list of strings, find lengths of each of them
+names = ["scaler", "interviewbit"]
+len_list = []
+for name in names:
+  len_list.append(len(name))
+print(len_list)
+```
+
+```py
+# using list comprehension
+len_list = [len(name) for name in names]
+len_list = [("length", len(name)) for name in names]
+print(len_list)
+# with odd lengths
+len_list = [("length", len(name)) for name in names if len(name) % 2 == 1]
+print(len_list)
+```
+
+```py
+# sum of all even numbers from 1 to 100
+sum_even = sum([num for num in range(1, 101) if num % 2 == 0])
+print(sum_even)
+```