How do you find first occurrence of a character in a list Python?

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“python find first occurrence in list” Code Answer’s
Python answers related to “python find first occurrence in list”
Python queries related to “python find first occurrence in list”
Python: Get index of item in List
Python | First character occurrence from rear String
Python String – Find the index of first occurrence of substring
Example 1: Find index of First Occurrence of Substring
Example 2: Find index of First Occurrence of Substring after a specific position
python program to find first occurrence of a character in a string Example 1
How do you find the first occurrence of an element in a list?
How do you find the first occurrence of a string in a string in python?
Which method is used to get the first occurrence of specified element?

python by Comfortable Cormorant on Aug 21 2020 Comment

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python find first occurrence in list

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on Jun 11 2020 Comment

python get first occurrence in list

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find the first occurrence of item in a list in python

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Python: Get index of item in List

To find index of element in list in python, we are going to use a function list.index(),

list.index()

Python’s list data type provides this method to find the first index of a given element in list or a sub list i.e.

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list.index(x[, start[, end]])

Arguments :

x : Item to be searched in the list
start : If provided, search will start from this index. Default is 0.
end : If provided, search will end at this index. Default is the end of list.

Returns: A zero based index of first occurrence of given element in the list or range. If there is no such element then it raises a ValueError.

Important Point : list.index() returns the index in a 0 based manner i.e. first element in the list has index 0 and second element in index is 1.

Let’s use this function to find the indexes of a given item in the list,

Suppose we have a list of strings,

# List of strings list_of_elems = ['Hello', 'Ok', 'is', 'Ok', 'test', 'this', 'is', 'a', 'test', 'Ok']

Now let’s find the index of the first occurrence of item ‘Ok‘ in the list,

elem = 'Ok' # Find index position of first occurrence of 'Ok' in the list index_pos = list_of_elems.index(elem) print(f'First Index of element "{elem}" in the list : ', index_pos)

Output

First Index of element "Ok" in the list : 1

As in the list.index() we did not provided start & end arguments, so it searched for the ‘Ok‘ in the complete list. But returned the index position as soon as it encountered the first occurrence of ‘Ok‘ in the list.

But if searched item doesn’t exists in the list, then index() will raise ValueError. Therefore we need to be ready for this kind of scenario. For example,

list_of_elems = ['Hello', 'Ok', 'is', 'Ok', 'test', 'this', 'is', 'a', 'test', 'Ok'] elem = 'Why' try: index_pos = list_of_elems.index(elem) print(f'First Index of element "{elem}" in the list : ', index_pos) except ValueError as e: print(f'Element "{elem}" not found in the list: ', e)

Output

Element "Why" not found in the list: 'Why' is not in list

As ‘Why‘ was not present in the list, so list.index() raised ValueError.

Python | First character occurrence from rear String

There are many ways to find out the first index of element in String as python in its language provides index() function that returns the index of first occurrence of element in String. But if one desires to get the last occurrence of element in string, usually a longer method has to be applied. Lets discuss certain shorthands to achieve this particular task.

Method #1 : Using rfind()
This is usually the hack that we can employ to achieve this task. Employing string function rfind() to get the first element from right i.e last index of element in String.

# Python 3 code to demonstrate

# First character occurrence from rear String

# using rfind()

# initializing string

test_str = "Geeksforgeeks"

# printing original string

print ("The original string is : " + str(test_str))

# using rfind()

# to get last element occurrence

res = test_str.rfind('e')

# printing result

print ("The index of last element occurrence: " + str(res))

Output : The original string is : Geeksforgeeks The index of last element occurrence: 10

Method #2 : Using List Slice + index() + list()
One can convert the string to list using list() and then using list slicing we reverse the list and use the conventional index method to get the index of first occurrence of element. Due to reversed list, the last occurrence is returned rather than the first index of list.

# Python 3 code to demonstrate 
# First character occurrence from rear String 
# using List Slice + index() + list() 

# initializing string 

test_str = "Geeksforgeeks"

# printing original string 

print ("The original string is : " + str(test_str))

# using List Slice + index() + list() 
# First character occurrence from rear String 

test_str = list(test_str)

res = len(test_str) - 1 - test_str[::-1].index('e')

# printing result 

print ("The index of last element occurrence: " + str(res))

Output : The original string is : Geeksforgeeks The index of last element occurrence: 10

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Python String – Find the index of first occurrence of substring

To find the position of first occurrence of a string, you can use string.find() method.

index = string.find(substring, start, end)

where string is the string in which you have to find the index of first occurrence of substring. start and end are optional and are starting and ending positions respectively in which substring has to be found.

Example 1: Find index of First Occurrence of Substring

In the following example, we will take a string and try to find the first occurrence of substring prog.

Python Program

string = 'Python programming. Network programming.' substring = 'prog' index = string.find(substring) print(index)Run

Output

Example 2: Find index of First Occurrence of Substring after a specific position

In the following example, we will take a string and try to find the first occurrence of substring prog after position 12 in the string.

Python Program

string = 'Python programming. Network programming.' substring = 'prog' start = 12 index = string.find(substring, start) print(index)Run

Output

Now it has found index of the substring that occurred for the first time after start position.

Summary

In this tutorial of Python Examples, we learned how to find the index of substring in a string using str.find() function.

python program to find first occurrence of a character in a string Example 1

This python programallows the user to entera string and a character.

Please refer String article to understand everything about Python Strings.

# Python Program to check First Occurrence of a Character in a String string = input("Please enter your own String : ") char = input("Please enter your own Character : ") flag = 0 for i in range(len(string)): if(string[i] == char): flag = 1 break if(flag == 0): print("Sorry! We haven't found the Search Character in this string ") else: print("The first Occurrence of ", char, " is Found at Position " , i + 1)

Python first character occurrence in a string output

Please enter your own String : hello world Please enter your own Character : l The first Occurrence of l is Found at Position 3

Here, we usedFor Loopto iterate every character in a String. Inside the For Loop, we used theIf statementto check whether any character in str1 string is equal to character ch or not. If true, then flag = 1, andBreak statementexecuted.

string = hello world
ch = l
flag = 0

For Loop First Iteration: for i in range(11)
if(string[i] == char)
if(h == l) – Condition is false.

Second Iteration: for 1 in range(11)
if(e == l)– Condition is false.

Third Iteration: for 2 in range(11)
if(str[2] == ch) =>if(l == l) – Condition is True.

Flag = 1and breakstatement exit from the loop. Next, we used theIf Else Statementto check whether the flag value is equal to 0. Here, the condition is False. So, print inside the else blocks executed.

How do you find the first occurrence of an element in a list?

To find index of the first occurrence of an element in a given Python List, you can use index() method of List class with the element passed as argument. The index() method returns an integer that represents the index of first match of specified element in the List.

How do you find the first occurrence of a string in a string in python?

Use str. index() to find the first occurrence of a substring in a string. Call str. index(substr) with substr as the target substring in the string str .