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Section 15.2 Strings are Objects

Strings are objects in Python which means that there is a set of built-in functions that you can use to manipulate strings. You use dot-notation to invoke the functions on a string object such as sentence.lower(). The function lower() returns a new string with all of the characters in the original string set to lowercase. The function capitalize() will return a new string with the first letter of the string capitalized.
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Subsection 15.2.1 Getting Part of a String

A string has characters in a sequence. Each character is at a position or index which starts with 0 as shown below. An index is the term for a number associated with a position in a collection of values like a string.
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Figure 15.2.1. A string with the position (index) shown above each character
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A slice is a way to get part of a string. One way to use a slice is to do stringName[num]. This will return a new string with just the character at that position in the string.
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A slice with two values separated with a : between them returns a new string with the characters from the given start position to the one before the given end position.
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Check Your Understanding
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Checkpoint 15.2.2.

What will be printed when the following executes?
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str = "This is the end"
str = str[1:4]
print(str)
  • This is the end
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  • This would be true if we were printing the value of str and we had not changed it on line 2.
  • This
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  • This would be true if the first position was 1 and the substring included the character at the end position, but the first character in a string is at position 0 and the substring won’t include the character at the last position.
  • his
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  • This will return a string that starts at position 1 and ends at position 3.
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Checkpoint 15.2.3.

What will be printed when the following executes?
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str = "This is the end"
str = str[5]
print(str)
  • This will print the character at position 5 in the string which is i. Remember that the first character is at position 0.
  • This would be true if the first character was at position 1 instead of 0.
  • is the end
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  • This would be true if it returned from the given position to the end of the string, but that isn’t what it does.
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Subsection 15.2.2 Some Other String Functions

The len(string) function takes a string as input and returns the number of characters in the string including spaces.
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The find(string) function takes a string as input and returns the index where that string is found in the current string. If the string isn’t found it returns -1.
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Note 15.2.4.

The find function will return the first position it finds the given string in. Notice that above it printed 2 which means it found the “is” in “This” first.
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Check your understanding
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Checkpoint 15.2.5.

Given the following code segment, what will be printed?
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street = "125 Main Street"
print(len(street))
  • 13
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  • Don’t forget to include the spaces in the count.
  • 15
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  • The len function returns the number of elements in the string including spaces.
  • 10
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  • This would be true if the len function only returned the number of alphabetic characters, but it includes all including spaces.
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Checkpoint 15.2.6.

What will be printed when the following executes?
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str = "His shirt is red"
pos = str.find("is")
print(pos)
  • The find function returns the index of the first position that contains the given string.
  • This would be true if it was pos = str.find(" is").
  • 10
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  • This would be true if it was pos = str.find(" is") and the first position was 1, but it is 0.
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Checkpoint 15.2.7.

Write the code to evaluate the length of the string "I like green eggs" and print it. It should print "The length is 17".
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Answer.
# DECLARE VARIABLES
sentence = 'I like green eggs'
# PRINT RESULT
print('The length is ' + str(len(sentence)))
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