Lecture 2 (Spring 2023)

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Required readings

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• Sections 2.4 – 2.8
• Chapter 3

Strings

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Strings are sequences of case-sensitive characters, used to hold text-like data. Strings have many operations defined on them:

• concatenation. (
  <str> + <str>
  ) joins two strings together.

s1 = "hello"
s2 = "world"
s3 = s1 + s2       # s3 = "helloworld"
s4 = s1 + " " + s2 # s4 = "hello world"

• multiplication. (
  <str> * <int>
  ) repeats a string multiple times.

s1 = "hello"
s2 = s1 * 4   # s2 = "hellohellohellohello"

We used the same operator on different object types, and those operators performed different functions. Operator overloading is when operations have different functions depending on the object types provided to them.

Other string operations:

• len
  . returns the length of a string.
• s1 in s2
  .
  True
  if
  s1
  is a substring of
  s2
  otherwise
  False
  .
• Comparisons (
  ==
  ,
  <
  ,
  >
  ). Greater than and less than are based on Unicode order.

Indexing and slicing

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Strings are immutable

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Strings as output: f-strings

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String as input:

input()

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Booleans, conditionals, and branching

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Iteration (looping)

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for

loops,

range

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while

loops

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break

and

continue

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Guess-and-check algorithms

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