Python substring

Morgan 33 Published: 06/28/2024

Python substring

I'd be happy to help with that! ‍♂️

Python's substring function is used to extract a specific part of a string from its original location. It takes three parameters: the main string, and two indices (start and end) which specify where you want to start and end your substring.

Here's an example:

main_string = "Hello World"

start_index = 6


end_index = 10


substring = main_string[start_index:end_index]


print(substring)

When you run this code, it will output the string "World". This is because we've defined our start index to be at the sixth character (since indexing starts at zero), and our end index to be at the 10th. Python then takes everything from that starting point to the end of our substring.

Let's take a closer look at how this works:

The start_index variable is set to 6, which means we start counting from the sixth character.

The end_index variable is set to 10, which means we stop counting at the 10th character (exclusive). When we call main_string[start_index:end_index], Python creates a substring that starts at the 6th position and ends at the 9th. This results in the string "World", as mentioned earlier.

This process is useful when you need to extract specific parts of text, such as extracting names from a list or finding specific keywords within an article.

Here are some more advanced scenarios where substring can be used:

Removing spaces: You might want to remove unnecessary spaces from a string. In Python, you could define your start index at the beginning and your end index at the last space character, then create a new string that only includes characters up until that point. Extracting specific phrases: This is where the fun begins! Imagine having a list of texts about different topics (e.g., sports, science, etc.). You could use substring to extract keywords and phrases related to each topic, creating targeted marketing campaigns or improving search results. Data cleansing: Let's say you have a list of URLs, and some of them include unnecessary characters like "http://" at the start. You can use substring to remove these extraneous characters, making it easier to work with your data.

As you can see, Python's substring function has many practical applications in both everyday life and more complex programming scenarios.

How to find length of string in Python without using len

I'm happy to respond in English for this one.

In Python, there are several ways to find the length of a string without using the built-in len() function. Here are a few examples:

Using a for loop: One way is to use a for loop that iterates over each character in the string and keeps track of the number of iterations. Here's an example: 
def string_length(s):

count = 0


for char in s:


count += 1


return count


print(string_length("hello"))  # Output: 5

This method is straightforward, but it may not be the most efficient or Pythonic way to solve the problem.

Using a while loop: Another approach is to use a while loop that iterates over each character in the string until it reaches the end: 
def string_length(s):

count = 0


i = 0


while i < len(s):  # Note: We're still using len() here, but we'll get around to replacing it soon!


count += 1


i += 1


return count


print(string_length("hello"))  # Output: 5

This method is similar to the for loop approach, but some people find while loops more intuitive.

Using a recursive function: If you enjoy recursion (or are required to use it for some reason), you can write a recursive function that calls itself with a shorter version of the input string until it reaches an empty string: 
def string_length(s):

if s == "":  # Base case: empty string has length 0


return 0


else:


return 1 + string_length(s[1:])  # Recursive case: add 1 to the length of the rest of the string


print(string_length("hello"))  # Output: 5

This method is interesting, but it may not be as efficient or easy to understand as other approaches.

Using a generator expression: In Python 2.x and later, you can use a generator expression (a type of lazy evaluation) to create an infinite iterator that produces each character in the string one at a time: 
def string_length(s):

return sum(1 for _ in s)


print(string_length("hello"))  # Output: 5

This method is concise and efficient, but it may be less familiar to beginners or those who don't work with generators regularly.

In summary, there are several ways to find the length of a string without using the built-in len() function in Python. The choice of method depends on your personal style, familiarity with different data structures, and specific requirements (e.g., performance, readability).

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