Week 5 - Taking a deeper dive into Python Strings

Liaw Bei Le · April 22, 2021

Learning   Python   Practices   Cheatsheets   References   Reflections

Previously, I learnt the attributes of different data types. - append, extend, pop, join for lists; split for strings.

  1. Today, I learnt more string attributes -
    • capitalize, title, upper, lower
    • index, find, search
    • count
    • startswith, endswith
    • strip
  2. String index & String slicing
    There are many ways to substring a string.
    This is called ‘slicing’. Also can reverse a string.
  3. Check if substring in string
  4. Iterate through a string or sub string
  5. Old method of string formatting using % (for reference only, I’ll be using f-strings instead)

Cheatsheets

Python Strings Guide

What I learnt:

1. String Attributes

  • For strings, I learnt how to use string.capitalize( ), string.title( ), string.upper( ), string.lower( ) attributes 
    x='hello there'
print(x.title())
print(x.capitalize())
print(x.upper())
print(x.lower())

    Output:

    Hello There
Hello there
HELLO THERE
hello there
  • string.index( ), string.find( ), string.search( ) attributes
    5 Ways to Find the Index of a Substring in Python
    1. str.find()
    2. str.rfind()
    3. str.index()
    4. str.rindex()
    5. re.search()
    • Using .index() 
      sentence = 'Python programming is fun.'
result = sentence.index('is fun')
print("Substring 'is fun':", result)

      Output:

      Substring 'is fun': 19
    • Using .find() 
      "this is fun".find("fun")

      Output:

      8
  • string.count( ) attribute 
    astring = "Hello world!"
print(astring.count("l"))

    Output:

    3
  • string.startswith( ), string.endswith( ) attribute
    • Example 1: 
        astring = "Hello world!"
  print(astring.startswith("Hello"))
  print(astring.endswith("asdfasdfasdf"))

      Output:

        True
  False
    • Example 2: 
        if "substring".startswith("sub"):
  print("substring starts with sub")

      Output:

        substring starts with sub
  • string.strip(‘chars’) attribute 
    string = '  xoxo love xoxo   '
# Leading and trailing whitespaces are removed
print(string.strip())
# All <whitespace>,x,o,e characters in the left and right of string are removed
print(string.strip(' xoe'))
# Argument doesn't contain space
# No characters are removed.
print(string.strip('stx'))
# Argument doesn't contain space
# 'an' is removed.
string = 'android is awesome'
print(string.strip('an'))

2. String index, String Slicing & Reversing a string

  • string_name[index] to find character in the stated position.
  • index can be negative from -1, -2 etc… to get character in the last position and so on working backwards. 
    student_name='Colette'
if student_name[0].lower="c":
  print("Winner! Name starts with 'C'")
    1. string[start:end]
      Get all characters from index start to end-1
    2. string[:end]
      Get all characters from the beginning of the string to end-1
    3. string[start:]
      Get all characters from index start to the end of the string
    4. string[start:end:step]
    • Example 1:
      Get all characters from start to end-1 discounting 
      s = "Hey there! what should this string be?"
print(f"Length of s = {len(s)}")
print(f"The first occurrence of the letter a = {s.index('a')}")
print(f"a occurs {s.count('a')} times")
# Slicing the string into bits
print(f"The first five characters are '{s[:5]}'") # Start to 5
print(f"The next five characters are '{s[5:10]}'")  # 5 to 10
print(f"The thirteenth character is '{s[12]}'") # Just number 12
print(f"The characters with odd index are '{s[1::2]}'") #(0-based indexing)

      Output:

      Length of s = 38
The first occurrence of the letter a = 13
a occurs 1 times
The first five characters are 'Hey t'
The next five characters are 'here!'
The thirteenth character is 'h'
The characters with odd index are 'e hr!wa hudti tigb?'
    • Example 2:
      Read a string backwards 
      astring = "!figt"
print(astring[::-1])

      Output:

      tgif!

3. Check if substring in string

if "fun" in "this is fun":
    print("'this is fun' contains the word 'fun'.")

Output:

this is fun contains the word fun.

4. Iterate through a string or sub string

Use for variable_name in string_name or
for variable_name in string_name[x:x:x]

for item in her_name:

for letter in vegetable_name:

Thoughts

I managed to learn many new attributes of strings today, which is really great to know! String indexing and slicing is especially complicated due to the numbering(s) and I did read up more to learn more about how slice positions work.

Additional Resource(s):

Slice positions explained

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