Extract value from string Python

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Python: Tips of the Day

Serialization:

Sometimes you may need to save your Python object locally for later use or Network transfers. Python has fantastic libraries for serialization such as Json and Pickle.

Serialization is storing data structures in the program so they don't just disappear after the program is terminated.

There is also marshal library but it's more primitive and can't handle certain techniques such as class instances and recursion. Marshal is closer to json in its scope of serialization.

So, when would you use pickle, cpickle, json or ujson?

cpickle and ujson are faster versions of respective libraries that take advantage of C implementations in Python. So they'd always be favorable for speed reasons.

Apart from that, json is a more secure and readable version of serialization than pickle which comes at a cost of speed.

While you can take care of almost any data structure in Python with Json it gets inefficient with large files or uncommon objects. Pickle on the other hand operates in a sweet spot where you'd like to work with large files (multiple GBs) and still don't want to be bothered with database solutions.

The thing is depending on your application, you may have to watch out for security vulnerabilities pickle introduces to the system so it's usually wise to seek out json or database solutions before resorting to pickle when possible.

The following tool visualize what the computer is doing step-by-step as it executes the said program:


Python Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous: Write a Python program to sort a given matrix in ascending order according to the sum of its rows.
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What is the difficulty level of this exercise?

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Python: Tips of the Day

Serialization:

Sometimes you may need to save your Python object locally for later use or Network transfers. Python has fantastic libraries for serialization such as Json and Pickle.

Serialization is storing data structures in the program so they don't just disappear after the program is terminated.

There is also marshal library but it's more primitive and can't handle certain techniques such as class instances and recursion. Marshal is closer to json in its scope of serialization.

So, when would you use pickle, cpickle, json or ujson?

cpickle and ujson are faster versions of respective libraries that take advantage of C implementations in Python. So they'd always be favorable for speed reasons.

Apart from that, json is a more secure and readable version of serialization than pickle which comes at a cost of speed.

While you can take care of almost any data structure in Python with Json it gets inefficient with large files or uncommon objects. Pickle on the other hand operates in a sweet spot where you'd like to work with large files (multiple GBs) and still don't want to be bothered with database solutions.

The thing is depending on your application, you may have to watch out for security vulnerabilities pickle introduces to the system so it's usually wise to seek out json or database solutions before resorting to pickle when possible.

If you have a string that contains numbers and you want to get those numbers out, you can use the Python built-in functions int(), isdigit() to extract the integer values from the string. In this post, we will show you multiple methods to do that.

Output

Integer values in string are:  [100, 120, 10]

Solution 1: Using split(), isdigit() and List comprehension

Given a string, the task is to extract only the integers from the string and print them. This can be done using the split() method and isdigit() method. The split() method returns a list of substrings that are separated by a given delimiter. The isdigit() method returns True if all characters in the string are digits and there is at least one character, False otherwise.

List comprehension can be used to iterate over the list returned by the split() method and isdigit() method to check if each substring is a digit or not. If it is a digit, then it can be added to a list. Finally, the list of integers can be printed.

Code example 1

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = [int(x) for x in my_str.split() if x.isdigit()]

print(result)

Output

[10, 50, 20, 52]

The above code sets the variable my_str to a string containing numbers and words. It then uses a list comprehension to create a new list, result, which contains only the numbers from my_str, converted to integers. Finally, it prints the contents of the result.

Code example 2: without using split() - This can be helpful when you don't have spaces between numbers and words

my_str = "abc1de4fg8ij5k7"

result = [int(x) for x in my_str if x.isdigit()]

print(result)

Output

[1, 4, 8, 5, 7]

Solution 2: Using For loop

We can also use Python For loop to iterate over the string words and characters and can extract integer values from it. Below are some code examples that will help you to understand it.

Example1: Using for loop and split

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = []

for x in my_str.split():
    if(x.isdigit()):
        result.append(int(x))
    
print(result)

Output

[10, 50, 20, 52]

Example 2: Without using split() function 

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = []

for x in my_str:
    if(x.isdigit()):
        result.append(int(x))
    
print(result)

Output

[1, 0, 5, 0, 2, 0, 5, 2]

Example 3

input_str = "abc1de4fg8ij5k7"

r = []
for x in input_str:
    if x.isdigit():
        r.append(int(x))
    
print(r)

Output

[1, 4, 8, 5, 7]

Solution 3: Using findall() function of regex re module

The re module in python has a findall() function which can be used to extract integer values from a string. The findall() function returns a list of all the matches it finds. The string can be either a literal string or a regular expression. If you want to extract only positive integers, you can use the following regular expression: [1-9][0-9]*

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = [int(x) for x in my_str.split() if x.isdigit()]

print(result)
1

Output

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = [int(x) for x in my_str.split() if x.isdigit()]

print(result)
2

In the above code example

  1. The first line imports the 're' module which provides regular expression tools.
  2. The second line defines a string variable called mystr.
  3. The third line uses the findall() function from the 're' module to find all instances of one or more digits in the string and stores them in the 'result' variable.
  4. The fourth line converts the 'result' variable from a list of strings to a list of integers.
  5. The fifth line prints the new list of integers.

Using filter(), map() and isdigit() function

In Python, the isdigit() method is used to check whether the given string is a digit or not. This function is used in conjunction with map() and filter() functions to extract only the integer values from a string. The map() function applies isdigit() function to each element of the given iterable (i.e. list, tuple, etc.) and returns a list of the results. The filter() function filters the given iterable by eliminating the elements for which the isdigit() method returns False.

Thus, to extract only the integer values from a string, we need to use the map() and filter() functions along with the isdigit() method.

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = [int(x) for x in my_str.split() if x.isdigit()]

print(result)
3

Output

my_str = "There are 10 rabbits, 50 dogs and 20 cats in this area 52"

result = [int(x) for x in my_str.split() if x.isdigit()]

print(result)
4

In the above code example, the map() function applies the int function to every element in the my_str list. The filter function checks if every element in the my_str list is a digit and returns a list of only the digit elements. Finally, the print function prints out the resulting list.

How do I extract a specific value from a string in Python?

Summary: To extract numbers from a given string in Python you can use one of the following methods:.
Use the regex module..
Use split() and append() functions on a list..
Use a List Comprehension with isdigit() and split() functions..
Use the num_from_string module..

How do I extract values from a string?

When you are working with data stored as a string, you can extract substrings from the total string. This extraction is done by specifying the offset within the string, indicating from which position you want to extract the substring. Position number from which to start extracting.

How do I extract specific text in Python?

How to extract specific portions of a text file using Python.
Make sure you're using Python 3..
Reading data from a text file..
Using "with open".
Reading text files line-by-line..
Storing text data in a variable..
Searching text for a substring..
Incorporating regular expressions..
Putting it all together..

How do I extract a string after a specific string in Python?

Using partition() to get string after occurrence of given substring. The partition function can be used to perform this task in which we just return the part of partition occurring after the partition word.