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Python: Find the index of a given string at which a given substring starts

Python String: Exercise-81 with Solution

Write a Python program to find the index of a given string at which a given substring starts. If the substring is not found in the given string return 'Not found'.

Sample Solution:-

Python Code:

def find_Index(str1, pos):
    if len(pos) > len(str1):
        return 'Not found'

    for i in range(len(str1)):

        for j in range(len(pos)):

            if str1[i + j] == pos[j] and j == len(pos) - 1:
                return i
                
            elif str1[i + j] != pos[j]:
                break

    return 'Not found'
print(find_Index("Python Exercises", "Ex"))
print(find_Index("Python Exercises", "yt"))
print(find_Index("Python Exercises", "PY"))

Sample Output:

7
1
Not found

Flowchart:

Flowchart: Find the index of a given string at which a given substring starts.

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Python: Tips of the Day

Check if a given key already exists in a dictionary:

In is the intended way to test for the existence of a key in a dict.

d = {"key1": 10, "key2": 23}

if "key1" in d:
    print("this will execute")

if "nonexistent key" in d:
    print("this will not")

If you wanted a default, you can always use dict.get():

d = dict()

for i in range(100):
    key = i % 10
    d[key] = d.get(key, 0) + 1

and if you wanted to always ensure a default value for any key you can either use dict.setdefault() repeatedly or defaultdict from the collections module, like so:

from collections import defaultdict

d = defaultdict(int)

for i in range(100):
    d[i % 10] += 1

but in general, the in keyword is the best way to do it.

Ref: https://bit.ly/2XPMRyz