Basic String Methods

In this lesson, we will be looking a string methods that deal with searching, checking the status, and editing strings.

This is not an exhaustive list of all methods with strings. You check out the list of methods here.

Methods: set of code belonging to a certain data/object

• String and List data types have special methods only for them

• Usually, we need a period before the method name to use them

Example:

print('Hello {}!'.format('World'))

.format() is a string method!

Return: certain methods and functions have the ability to return a value/result after its operations

• This is useful when we assign the result to a variable

• Built-in functions like: len(), max(), min(), int(), float() all return a new value so that we can assign the result to a variable or update an existing variable

Search Related Methods

Recall: Index starts at 0

string_data.count(_str_arg_)

• Returns how many time the string argument occurs in the given variable

string_data.find(_str_arg_)

• Returns the location of where the string argument was found. If not found, returns -1

string_data.index(_str_arg_)

• Same as find(), but raises an exception if str not found.

# Search Related Methods Examples

example = 'hello world!'
result_1 = example.count('e') # is 1
result_2 = example.count('l') # (single lowercase L) is 3
result_3 = example.count('ll') # (double lowercase L) is 1
print('result_1:', result_1)
print('result_2:', result_2)
print('result_3:', result_3)
print('-'*64)

result_4 = example.find('d') # is 10 … found at index 10
result_5 = example.find('z') # is -1 … not found
result_6 = example.find('or') # is 7 … ‘or’ begins at index 7
print('result_4:', result_4)
print('result_5:', result_5)
print('result_6:', result_6)
print('-'*64)

result_7 = example.index('d') # is 10 … found at index 10
print('result_7:', result_7)
result_8 = example.index('or') # is 7 … ‘or’ begins at index 7
print('result_8:', result_8)
result_9 = example.index('z') # is an error
print('result_9:', result_9)
print('-'*64)

result_1: 1
result_2: 3
result_3: 1
----------------------------------------------------------------
result_4: 10
result_5: -1
result_6: 7
----------------------------------------------------------------
result_7: 10
result_8: 7



---------------------------------------------------------------------------

ValueError                                Traceback (most recent call last)

<ipython-input-11-3bf5d49914e1> in <module>
     22 result_8 = example.index('or') # is 7 … ‘or’ begins at index 7
     23 print('result_8:', result_8)
---> 24 result_9 = example.index('z') # is an error
     25 print('result_9:', result_9)
     26 print('-'*64)


ValueError: substring not found

String Status Methods

These methods will all either return True or False.

string_data.isalnum()

• Checks iff alpha+numeric, no spaces or no special characters

string_data.isalpha()

• Checks iff alpha, no spaces, no numbers or no special characters

string_data.islower()

• Checks iff all characters are lowercased, doesn’t check whitespaces

string_data.isupper()

• Check iff all characters are uppercased, doesn’t check whitespaces

string_data.isdigit()

• Checks iff numeric, no spaces or no special characters, ignores unicode majority of the time, this is preferred over .isnumeric() and .isdecimal()

# String Status Methods Example

example1 = 'abc123'
example2 = '123'
example3 = 'HELLO'

print('example1.isalnum():', example1.isalnum()) # outputs True
print('example1.isalpha():', example1.isalpha()) # outputs False

print('example3.islower():', example3.islower()) # outputs False
print('example3.isupper():', example3.isupper()) # outputs True

print('example2.isdigit():', example2.isdigit()) # outputs True
print('example1.isdigit():', example1.isdigit()) # outputs False

example1.isalnum(): True
example1.isalpha(): False
example3.islower(): False
example3.isupper(): True
example2.isdigit(): True
example1.isdigit(): False

String Editing Methods

These methods will return a new string

string_data.capitalize()

• Capitalizes the first letter of a string

string_data.lower()

• Returns with all characters in the string lowercased

string_data.upper()

• Returns with all characters in the string uppercased

# Editing Strings Example
# string variables must be updated with new values if you want to modify it

example = 'hello, world!'
example = example.capitalize() # example : ‘Hello, world!’
print('example:', example)

example = example.upper() # example : ‘HELLO, WORLD!’
print('example:', example)

example = example.lower() # example : ‘hello, world!’
print('example:', example)

example: Hello, world!
example: HELLO, WORLD!
example: hello, world!