01 PDT - 06 String Methods

Method is a function that is built into a function used to perform actions on a piece of data. They are followed by a () parenthesis, as they may need additional data to work. (need to check documentation for more)

String Methods Covered:

1. Case Modification:

   • upper(): Converts all characters to uppercase.
   • lower(): Converts all characters to lowercase.
   • swapcase(): Swaps case (lower to upper and vice versa).
   • title(): Converts the first character of each word to uppercase.
   • capitalize(): Capitalizes the first character of the string.

2. Cleaning Strings:

   • rstrip(): Removes trailing whitespace.
   • lstrip(): Removes leading whitespace.
   • strip(): Removes both leading and trailing whitespace.
   • removeprefix(): Removes a specified prefix from the string.
   • removesuffix(): Removes a specified suffix from the string.

3. Searching for Text:

   • find(): Returns the index of the first occurrence of a substring (returns -1 if not found).
   • index(): Similar to find(), but raises an error if the substring isn’t found.

4. Search and Replace:

   • replace(): Replaces occurrences of a substring with a new one.

5. Splitting Strings:

   • split(): Splits the string into a list at each occurrence of a specified delimiter (defaults to whitespace).
   • splitlines(): Splits the string into a list at each newline character (\n).

6. Resizing Strings:

   • center(): Centers the string within a given width, padding with spaces.
   • ljust(): Left-aligns the string within a given width, padding with spaces.
   • rjust(): Right-aligns the string within a given width, padding with spaces.

7. Checking Character Types:

   • isalpha(): Returns True if all characters are alphabetic.
   • isnumeric(): Returns True if all characters are numeric.

8. Other Utility:

   • join(): Joins elements of an iterable (e.g., a list) into a single string, using the string as a separator.

Changing Case

The title() method capitalizes the first letter of each word.

variable.title()
print(variable.title())

The . after the variable tells Python to apply the title() method on it.

variable.upper()
variable.lower()
variable.swapcase()

lower() is useful for handling user input data, while swapcase() changes uppercase to lowercase and vice versa.

To adjust mis-typed spacing and capitalization in a string:

name = name.capitalize()    # Capitalizes the first letter
name = name.title()         # Converts to title case
name = name.title().strip() # Strips leading and trailing spaces
name = name.strip()         # Removes spaces on both sides

Everything in one line:

name = input("What's your name? ").title().strip()
print(f"Hello, {name}", name, sep=' ', end="\n")
name = input("Please type your name: ").strip().title()

Stripping White Space / Removing Prefix

When comparing two values, extra whitespace can lead to mismatches. It’s a good idea to handle whitespace before storing data:

variable.rstrip() 
variable.lstrip()
variable.strip()

To remove prefixes:

url = 'https://nostarch.com'
url.removeprefix('https://')
url.removesuffix('.com')

Searching for Text

• find(): Returns the index of the first occurrence of a substring, or -1 if not found.

s.find(pattern)
s.find(pattern, start, end)

• index(): Works like find(), but raises an error if the substring is not found.

s.index(pattern)
s.index(pattern, start, end)

1. Using find():

text = "Hello, welcome to the world of Python."

# Find the first occurrence of 'welcome'
position = text.find("welcome")
print(position)  # Output: 7 (index of 'w' in 'welcome')

# Find a substring within a slice
position = text.find("world", 10, 30)  # Searching in the range from index 10 to 30
print(position)  # Output: 20 (index of 'w' in 'world')

If the pattern is not found, find() will return -1:

position = text.find("Java")
print(position)  # Output: -1 (since 'Java' isn't in the string)

2. Using index():

# Using index to find 'Python'
position = text.index("Python")
print(position)  # Output: 33 (index of 'P' in 'Python')

# Using index with a slice
position = text.index("world", 10, 30)
print(position)  # Output: 20 (index of 'w' in 'world')

If the pattern is not found, index() will raise an error:

try:
    position = text.index("Java")
except ValueError:
    print("Pattern not found!")  # Output: Pattern not found!

Search and Replace

Returns a copy of s with fromstr replaced by tostr:

s.replace(fromstr, tostr)
s.replace(fromstr, tostr, n)  # Replaces at most n copies

Note: Strings are immutable, so replace() returns a new string.

Splitting a String

Split a string into substrings. For example:

first, last = name.split(" ")
print(f"Hey, {first}, How are you?")

For CSV-like data, use a delimiter like ,:

columns = s.split(",")  # Split by comma
columns = s.split(" : ", n)  # Split at most n parts

Example:

csline = "6,7,8"
csvline.split(",")  # ['6', '7', '8']

Resizing Strings

Resize strings to a specified width, using padding:

s.center(n)  # Centers string
s.center(n, "*")  # Centers with stars

s.ljust(n)    # Left justifies string
s.ljust(n, "*")  # Left justify with stars

s.rjust(n)    # Right justifies string
s.rjust(n, "*")  # Right justify with stars

Checking Nature of Characters in a String

Check if all characters in the string are alphabetic or numeric:

s.isalpha()    # Checks if all characters are alphabetic
s.isnumeric()  # Checks if all characters are numeric

join(): Joins elements of an iterable (e.g., a list, tuple) into a single string, using the string that calls the method as the separator.

words = ['Hello', 'world', 'Python']
sentence = ' '.join(words)  # Joins with space
print(sentence)  # Output: "Hello world Python"

# Join with a different separator
sentence = '-'.join(words)  # Joins with a hyphen
print(sentence)  # Output: "Hello-world-Python"