CodeBlanks Logo Icon CodeBlanks
Login Register

find and index

Learn searching with find and index.

find and index

find returns the first position of a substring; if not found, it returns -1:

"hello".find("l")   # 2
"hello".find("x")   # -1

index does the same but raises ValueError if not found. So find is safer.

Both return the index of the first match; to find later matches, use the start parameter.

Searching with find

The second parameter of find is the start position:

s = "hello"
s.find("l")        # 2
s.find("l", 3)     # 3

This is used to find the next match. With a loop you can find all match positions.

This method is very useful for searching log files.

Practice Find a position with find

Assign "hello world" to text. Assign text.find("world") to pos. Then print print(pos).

Starter code

main.py
# Find a position with find

Sample solution

main.py
text = "hello world"
pos = text.find("world")
print(pos)

Expected output

6

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Match find and index

Term Meaning
find Returns -1 if missing
index Raises ValueError if missing
first match Return position
start parameter Next match

2 Complete the find call

Question 
pos = "hello".____("l")
Answer 
pos = "hello".find("l")

Explanation: find("l") gives the position of 'l'.

3 What does "hello".find("x") return?

  • -1 Correct answer
  • Raises an error
  • None
  • 0

Explanation: find returns -1 when not found.

All lessons in Beginner

1 Python basics

  1. What is Python?
  2. REPL and print
  3. Comments
  4. Indentation blocks
  5. python -c and scripts
  6. Summary - Python basics

2 Variables

  1. Variable assignment
  2. Multiple assignment
  3. Naming variables
  4. id and type
  5. Swapping variables
  6. Summary - Variables

3 Data types

  1. int and float
  2. bool
  3. str basics
  4. None
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Membership and identity
  6. Summary - Operators

6 String basics

  1. f-string
  2. Concatenation
  3. str.format
  4. Raw strings
  5. Triple-quote
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. elif and else
  3. Nested if
  4. Truthiness
  5. Conditional expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. range
  3. The while loop
  4. break and continue
  5. Loop else
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Lists

  1. Declaring lists
  2. Index and slice
  3. List methods
  4. in and count
  5. Sorting lists
  6. Summary - Lists

11 List comprehension

  1. Comprehension basics
  2. Filtered comprehension
  3. Dict and set comprehension
  4. Nested comprehension
  5. Generator expression
  6. Summary - List comprehension

12 Tuple, set and dict

  1. Tuple
  2. Set
  3. Dict basics
  4. Dict methods
  5. Dict comprehension
  6. Summary - Tuple, set and dict

13 Functions

  1. def
  2. return
  3. Docstring
  4. Default parameters
  5. *args and **kwargs
  6. Summary - Functions

14 Function parameters

  1. Positional parameters
  2. Keyword parameters
  3. Keyword-only
  4. Positional-only
  5. Type hints basics
  6. Summary - Function parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string methods

  1. split and join
  2. strip, lstrip, rstrip
  3. replace
  4. find and index
  5. startswith, endswith
  6. Summary - Advanced strings

17 Input and output

  1. input()
  2. int/float conversion
  3. print parameters
  4. f-string formatting
  5. sys.argv
  6. Summary - Input and output

18 Error handling

  1. try/except
  2. else and finally
  3. raise
  4. Exception hierarchy
  5. Custom exceptions
  6. Summary - Error handling

19 Modules

  1. import
  2. from import
  3. as alias
  4. __name__ == '__main__'
  5. Standard library
  6. Summary - Modules

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together