Python for each word in string

Given a String comprising of many words separated by space, write a Python program to iterate over these words of the string.

Examples:

Input: str = “GeeksforGeeks is a computer science portal for Geeks” 
Output: GeeksforGeeks is a computer science portal for Geeks 

Input: str = “Geeks for Geeks” 
Output: Geeks for Geeks

Method 1: Using split() Using split() function, we can split the string into a list of words and is the most generic and recommended method if one wished to accomplish this particular task. But the drawback is that it fails in the cases in string contains punctuation marks. 

The original string is : GeeksforGeeks is a computer science portal for Geeks

The words of string are
GeeksforGeeks
is
a
computer
science
portal
for
Geeks

Time complexity: O(n)
Auxiliary Space: O(n)

Method 2: Using re.findall() In the cases which contain all the special characters and punctuation marks, as discussed above, the conventional method of finding words in a string using split can fail and hence requires regular expressions to perform this task. findall() function returns the list after filtering the string and extracting words ignoring punctuation marks. 

The original string is : GeeksforGeeks is a computer science portal for Geeks !!!

The words of string are
GeeksforGeeks
is
a
computer
science
portal
for
Geeks

Method 3: Using for loop and string slicing

The original string is: GeeksforGeeks is a computer science portal for Geeks
GeeksforGeeks
is
a
computer
science
portal
for
Geeks

This approach uses a for loop to iterate through the characters in the string and a variable to keep track of the starting index of the current word. When a space is encountered, the current word is printed and the starting index is updated to the next character. The last word in the string is printed outside the loop.

Time Complexity: O(n)
Auxiliary Space : O(n) 

Method 4: Using the split() method with a regular expression

Use the split() method with a regular expression to split the string into words

Step-by-step approach:

• Initialize a list to store the words extracted from the string.
• Use the split() method with a regular expression to split the string into words.
• Iterate over the words and append them to the list.
• Print the list of words.

Follow the below steps to implement the above idea:

The original string is : GeeksforGeeks is a computer science portal for Geeks !!!

The words of string are
GeeksforGeeks
is
a
computer
science
portal
for
Geeks

Time complexity: O(n), where n is the length of the input string.
Auxiliary space: O(n), where n is the length of the input string.

In this tutorial, you will find out different ways to iterate strings in Python. You could use a for loop, range in Python, slicing operator, and a few more methods to traverse the characters in a string.

Multiple Ways to Iterate Strings in Python

The following are various ways to iterate the chars in a Python string. Let’s first begin with the for loop method.

Using for loop to traverse a string

It is the most prominent and straightforward technique to iterate strings. Follow the below sample code:

"""
Python Program:
 Using for loop to iterate over a string in Python
"""
string_to_iterate = "Data Science"
for char in string_to_iterate:
   print(char)

The result of the above coding snippet is as follows:

D
a
t
a

S
c
i
e
n
c
e

Python range to iterate over a string

Another quite simple way to traverse the string is by using Python range function. This method lets us access string elements using the index.

Go through the sample code given below:

"""
Python Program:
 Using range() to iterate over a string in Python
"""
string_to_iterate = "Data Science"
for char_index in range(len(string_to_iterate)):
   print(string_to_iterate[char_index])

The result of the above coding snippet is as follows:

D
a
t
a

S
c
i
e
n
c
e

Slice operator to iterate strings partially

You can traverse a string as a substring by using the Python slice operator ([]). It cuts off a substring from the original string and thus allows to iterate over it partially.

The [] operator has the following syntax:

# Slicing Operator
string [starting index : ending index : step value]

To use this method, provide the starting and ending indices along with a step value and then traverse the string. Below is the example code that iterates over the first six letters of a string.

"""
Python Program:
 Using slice [] operator to iterate over a string partially
"""
string_to_iterate = "Python Data Science"
for char in string_to_iterate[0 : 6 : 1]:
   print(char)

The result of the above coding snippet is as follows:

P
y
t
h
o
n

You can take the slice operator usage further by using it to iterate over a string but leaving every alternate character. Check out the below example:

"""
Python Program:
 Using slice [] operator to iterate over a specific parts of a string
"""
string_to_iterate = "Python_Data_Science"
for char in string_to_iterate[ :  : 2]:
   print(char)

The result of the above coding snippet is as follows:

P
t
o
_
a
a
S
i
n
e

Traverse string backward using slice operator

If you pass a -ve step value and skipping the starting as well as ending indices, then you can iterate in the backward direction. Go through the given code sample.

"""
Python Program:
 Using slice [] operator to iterate string backward
"""
string_to_iterate = "Machine Learning"
for char in string_to_iterate[ :  : -1]:
   print(char)

The result of the above coding snippet is as follows:

g
n
i
n
r
a
e
L

e
n
i
h
c
a
M

Using indexing to iterate strings backward

Slice operator first generates a reversed string, and then we use the for loop to traverse it. Instead of doing it, we can use the indexing to iterate strings backward.

"""
Python Program:
 Using indexing to iterate string backward
"""
string_to_iterate = "Machine Learning"
char_index = len(string_to_iterate) - 1
while char_index >= 0:
   print(string_to_iterate[char_index])
   char_index -= 1

The result of the above coding snippet is as follows:

g
n
i
n
r
a
e
L

e
n
i
h
c
a
M

Alternatively, we can pass -ve index value and traverse the string backward. See the below example.

"""
Python Program:
 Using -ve index to iterate string backward
"""
string_to_iterate = "Learn Python"
char_index = 1
while char_index <= len(string_to_iterate):
   print(string_to_iterate[-char_index])
   char_index += 1

The result of the above coding snippet is as follows:

n
o
h
t
y
P

n
r
a
e
L

Summary – Program to iterate strings char by char

Let’s now consolidate all examples inside the Main() function and execute from there.

"""
Program:
 Python Program to iterate strings char by char
"""
def Main():
   string_to_iterate = "Data Science"
   for char in string_to_iterate:
      print(char)

   string_to_iterate = "Data Science"
   for char_index in range(len(string_to_iterate)):
      print(string_to_iterate[char_index])
      
   string_to_iterate = "Python Data Science"
   for char in string_to_iterate[0 : 6 : 1]:
      print(char)
      
   string_to_iterate = "Python_Data_Science"
   for char in string_to_iterate[ :  : 2]:
      print(char)

   string_to_iterate = "Machine Learning"
   for char in string_to_iterate[ :  : -1]:
      print(char)

   string_to_iterate = "Machine Learning"
   char_index = len(string_to_iterate) - 1
   while char_index >= 0:
      print(string_to_iterate[char_index])
      char_index -= 1

   string_to_iterate = "Learn Python"
   char_index = 1
   while char_index <= len(string_to_iterate):
      print(string_to_iterate[-char_index])
      char_index += 1

if __name__ == "__main__":
    Main()

The result of the above coding snippet is as follows:

D
a
t
a
 
S
c
i
e
n
c
e
D
a
t
a
 
S
c
i
e
n
c
e
P
y
t
h
o
n
P
t
o
_
a
a
S
i
n
e
g
n
i
n
r
a
e
L
 
e
n
i
h
c
a
M
g
n
i
n
r
a
e
L
 
e
n
i
h
c
a
M
n
o
h
t
y
P
 
n
r
a
e
L

In this Python tutorial, you will learn how to separate each word from a sentence in Python and then calculate the number of vowels in each word.

We shall be using certain string functions in Python like split() and lower()

The approach that we shall take

1. string.lower() to convert all the characters of the given string to their respective lower case.
2. string.split() method to separate words from a given sentence.
3. After we separate the words, it will be stored in a list called ‘words’.
4. Initialise a list called vowels that will contain all the vowels present in the English alphabet.
5. Iterate over the list words and initialise a counter that will count the number of vowels present in the word.
6. Start a nested loop that iterates over the word in question and check whether any character present in the word is a vowel or not
7. If a character is a vowel, increase the counter.
8. Print the word pertaining to the current iteration and the value of the counter associated with it(which contains the number of vowels in the sentence.
9. Keep on iterating till we have reached the end of the list words.

lower() function in Python

The lower function in Python is used to convert all the characters in string to lower case.

How does the lower function in Python work?

#Initialising some strings 
sentence1 = "The Sun Rises In THE EAST" 
sentence2 = "CODING in PYTHON is fun" 
sentence3 = "CODESPEEDY is a great website" 
sentence4 = "STRINGS are FUN to work with"
#prining the original sentences
print("The original strings are:-")
print(sentence1)
print(sentence2)
print(sentence3)
print(sentence4)
#printing the words of the sentences after converting them to lower case
print("After applying lower() function:-")
print(sentence1.lower())
print(sentence2.lower())
print(sentence3.lower())
print(sentence4.lower())

Output:-

The original strings are:-
The Sun Rises In THE EAST
CODING in PYTHON is fun
CODESPEEDY is a great website
STRINGS are FUN to work with
After applying lower() function:-
the sun rises in the east
coding in python is fun
codespeedy is a great website
strings are fun to work with

We can see that the lower() function in Python has converted words like ‘PYTHON’, ‘STRINGS’ to ‘python’ and ‘strings’ respectively.

We shall use this because the vowels list that we shall initialise later contains the vowels in lower case.

split() method in Python

split() method in Python breaks up a sentence into its constituent words on the basis of a particular separator. Here we are separating on the basis of the spaces in between the words.

How does the split() method in Python work?

#Initialising some strings
sentence1 = "sun rises in the east"
sentence2 = "coding in python is fun"
sentence3 = "codespeedy is a great website"
sentence4 = "strings are fun to work with"
#using the split function
words1 = sentence1.split()
words2 = sentence2.split()
words3 = sentence3.split()
words4 = sentence4.split()
#printing the words of the sentences after splitting them
print("The words of the first sentence are::", words1)
print("The words of the second sentence are::", words2)
print("The words of the third sentence are::", words3)
print("The words of the fourth sentence are::", words4)

Let’s look at the output:-

The words of the first sentence are:: ['sun', 'rises', 'in', 'the', 'east']
The words of the second sentence are:: ['coding', 'in', 'python', 'is', 'fun']
The words of the third sentence are:: ['codespeedy', 'is', 'a', 'great', 'website']
The words of the fourth sentence are:: ['strings', 'are', 'fun', 'to', 'work', 'with']

Here, Python has this facility via the split() function where we are getting a separate list based on the placement of whitespaces in between words.

Code and Output in Python

Study the code in Python given below and try to associate it with the approach mentioned above:-

s = "Python is a fun language and I really love coding in it" 
s = s.lower()
words = s.split() 
vowels = ['a','e','i','o','u'] 
for word in words: 
c = 0 
for i in range(0,len(word)): 
if word[i] in vowels: 
c+=1 
print(f"The number of vowels in the word '{word}'' is {c}")

The output for the code in Python given above is:-

The number of vowels in the word 'python'' is 1
The number of vowels in the word 'is'' is 1
The number of vowels in the word 'a'' is 1
The number of vowels in the word 'fun'' is 1
The number of vowels in the word 'language'' is 4
The number of vowels in the word 'and'' is 1
The number of vowels in the word 'i'' is 1
The number of vowels in the word 'really'' is 2
The number of vowels in the word 'love'' is 2
The number of vowels in the word 'coding'' is 2
The number of vowels in the word 'in'' is 1
The number of vowels in the word 'it'' is 1

Explanation of the Python code:-

• Convert all the characters in sentence to lower case using lower() function in Python.
• Split sentence up into its constituent words. We do so using the split() function  in Python which separates all the words from the string(‘sentence’) and stores it in a list (‘words’).
• Then initialise a list which contains all the vowels in the English alphabet [‘a’,’e’,’i’,’o’,’u’] so that we can check if the extracted character from the words of a sentence is a vowel or not.
• Iterate over the list words and then iterate over the string of the list words. We are nesting two for loops here.
• Initialise a counter and set the initial value to 0 in the outer loop
• In the inner loop, we compare every character of the word with the list vowels, hence checking if the character in question is a vowel or not.
• If the character is a vowel, we add 1 to the counter, hence counting the total number of vowels in the word that we are iterating against.
• When the inner loop is executed, print the word and the number of vowels in it.
• This process continues till all the elements of the list words are exhausted and we have essentially checked whether every character of every word is a vowel or not

I hope this Python tutorial was helpful!!

Python program to count the frequency of each word in a string :

In this python tutorial, we will learn how to count the frequency of each word in a user input string. The program will read all words, find out the number of occurrences for each word and print them out. It will also sort all the words alphabetically.

To solve this problem, we will use one dictionary. Dictionary is an unordered and mutable collection. It stores data as key-value pairs. Using any key, we can access its value. We can even modify the value for a specific key.

A python dictionary is written using a curly bracket. Each key and value are separated using colon (:), and all key-value pairs are separated with a comma (,).

We will use one dictionary to store the frequency of the word in a string. For this dictionary, the keys will be the words of the string, and the values will be the frequency for that word. For the string “hello world hello”, it will look as like below :

key - hello , value - 2
key - world , value - 1

As you can see, the word ‘hello’ appeared two times in the string. So, the value is 2 for the key ‘hello’. Similarly, for the key ‘world’, value is 1.

Also, it will print the value of the world before hello i.e. alphabetically.

Algorithm :

The algorithm for the above problem is like below :

1. Ask the user to enter the string. Store it in a variable.

2. Create one dictionary to store the frequency of each word in the string.

3. Read the words in the string one by one.

4. For each word, check if the dictionary has any key equal to the current word. If yes, increment the value for that key by 1. If not, add one new key-value pair with key equal to the word and value as 1.

5. Sort all keys in the dictionary alphabetically.

6. Finally, print out the frequency of each word to the user.

Let’s take a look at the program :

Python program :

#1
input_line = input("Enter a string : ")

#2
words_dict = {}

#3
for word in input_line.split():
    words_dict[word] = words_dict.get(word,0) + 1

#4
for key in sorted(words_dict):
  print("{} : {}".format(key,words_dict[key]))

The source code is shared on Github here.

Explanation :

The commented numbers in the above program denote the step-number below :

1. Ask the user to enter a string. Read and store it in the input_line variable.

2. Create one dictionary to store the key-value pair, where the key is the word and value is the frequency of that word. This is an empty dictionary. For creating an empty dictionary, we can use one empty curly braces.

3. Start scanning the words of the string one by one. Read the current frequency value for that word from the dictionary and add 1 to it or increment it by 1. If the current frequency is not available, return 0.

Here, we are splitting the string using ‘split()’ method. Python string split() method returns one list holding all the words in the string. Using the for loop, we are iterating through the list items, i.e. iterating the words of the string.

1. Sort all keys of the dictionary alphabetically. That means, sort all words contains in the dictionary alphabetically. The sorted() method is used to sort the keys in the dictionary.

Finally, print out the value of the frequency of each word.

Sample Output :

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As a part of text analytics, we frequently need to count words and assign weightage to them for processing in various algorithms, so in this article we will see how we can find the frequency of each word in a given sentence. We can do it with three approaches as shown below.

Using Counter

We can use the Counter() from collections module to get the frequency of the words. Here we first apply the split() to generate the words from the line and then apply the most_common ().

Example

 Live Demo

from collections import Counter
line_text = "Learn and practice and learn to practice"
freq = Counter(line_text.split()).most_common()
print(freq)

Running the above code gives us the following result −

[('and', 2), ('practice', 2), ('Learn', 1), ('learn', 1), ('to', 1)]

Using FreqDist()

The natural language tool kit provides the FreqDist function which shows the number of words in the string as well as the number of distinct words. Applying the most_common() gives us the frequency of each word.

Example

from nltk import FreqDist
text = "Learn and practice and learn to practice"
words = text.split()
fdist1 = FreqDist(words)
print(fdist1)
print(fdist1.most_common())

Running the above code gives us the following result −

<FreqDist with 5 samples and 7 outcomes>
[('and', 2), ('practice', 2), ('Learn', 1), ('learn', 1), ('to', 1)]

Using Dictionary

In this approach we store the words of the line in a dictionary. Then we apply the count() to get the frequency of each word. Then zip the words with the word frequency values. The final result is shown as a dictionary.

Example

 Live Demo

text = "Learn and practice and learn to practice"
words = []
words = text.split()
wfreq=[words.count(w) for w in words]
print(dict(zip(words,wfreq)))

Running the above code gives us the following result:

{'Learn': 1, 'and': 2, 'practice': 2, 'learn': 1, 'to': 1}