#set document(title: "8.3 Searching/testing strings", author: "OpenStax / XYZ Homework")
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== 8.3#h(0.6em)Searching/testing strings


  
    
=== Learning objectives


    By the end of this section you should be able to


    - Use the in operator to identify whether a given string contains a substring.
- Call the count() method to count the number of substrings in a given string.
- Search a string to find a substring using the find() method.
- Use the index() method to find the index of the first occurrence of a substring in a given string.
- Write a for loop on strings using in operator.


  
  
    
=== in operator


    The #strong[in] Boolean operator can be used to check if a string contains another string. in returns True if the first string exists in the second string, False otherwise.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[What is in the phrase?]


      #link("https://www.openstax.org/r/what-in-phrase")[What is the phrase?; ch 8, video 3]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Using in operator to find substrings]
]


  
  
    
=== For loop using in operator


    The in operator can be used to iterate over characters in a string using a for loop. In each for loop iteration, one character is read and will be the loop variable for that iteration.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[for loop using in operator]


      #link("https://www.openstax.org/r/for-loop-in-operator")[For loop using in operator; ch 8, video 4]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Using in operator within for loop]
]


  
  
    
=== count()


    The #strong[count()] method counts the number of occurrences of a substring in a given string. If the given substring does not exist in the given string, the value 0 is returned.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Counting the number of occurrences of a substring]


      #link("https://www.openstax.org/r/counting-substrings")[Counting the number of occurrences of a substring; ch 8, video 5]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Using count() to count the number of substrings]
]


  
  
    
=== find()


    The #strong[find()] method returns the index of the first occurrence of a substring in a given string. If the substring does not exist in the given string, the value of -1 is returned.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Finding the first index of a substring]


      #link("https://www.openstax.org/r/finding-substring-index")[Finding the first index of a substring; ch 8, video 6]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Using find() to locate a substring]
]


  
  
    
=== index()


    The #strong[index()] method performs similarly to the find() method in which the method returns the index of the first occurrence of a substring in a given string. The index() method assumes that the substring exists in the given string; otherwise, throws a ValueError.


    #examplebox("Example 1")[Getting the time's minute portion][
Consider a time value is given as part of a string using the format of "hh:mm" with "hh" representing the hour and "mm" representing the minutes. To retrieve only the string's minute portion, the following code can be used:


      
    time\_string = "The time is 12:50"
    index = time\_string.index(":")
    print(time\_string\[index+1:index+3\])
      The above code's output is:


      
    50
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Using index() to locate a substring]
]


  
  #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Finding all spaces]


    Write a program that, given a string, counts the number of space characters in the string. Also, print the given string with all spaces removed.


    
    Input: "This is great"
    
    Prints:
    2
    Thisisgreat
    s = "This is great"
]