String Indexing / slicing

What is indexing? Explain it and how it’s written and alternatives

Indexing = Allowing us to access elements of a sequence with [ ] (indexing operator) 

[start : end : step]

[1]

[:2:]

[1::]

[::9]

Find the first number in Credit_number = “1234 - 5687- 90123 - 4567”

print(Credit_number [0])

returns 1

Write to find first four digits of Credit_number = “1234 - 5687- 90123 - 4567”

print(Credit_number [0:4])

• This gives us start and stop, so first four elements 

• This will have us start start at one, and end 4

  • Indexing is exclusive, so if I see 4, it won't include that one. It will go up to 3)

• I can also write this as (:4) because I don’t need the zero 
  

Write to find 5th to 9th digits of Credit_number = “1234 - 5687- 90123 - 4567”

print(Credit_number [5:9])

• This will print 5678

  • (because dash counts as one)

Write to find all numbers up to 5th place of Credit_number = “1234 - 5687- 90123 - 4567”

print(Credit_number [:5])

• This will print everything up to the 5th place of a string 

• However, remeber that the first of these 5 is labeled as zero.

• Returns 1234-

Explain the inclusive / exclusive nature of indexing and slicing.

[start : end : step]

Start is inclusive

End is exclusive

if end is 5, it will count up to 4 places in the srring.

Write to find all numbers AFTER the 5th place of Credit_number = “1234 - 5687- 90123 - 4567”

print(Credit_number[5:]

5687- 90123 - 4567

Return the last number of the credit card number and explain why

print(Credit_number [-1])

Return the 3rd to last number of the credit card number and explain why

print(Credit_number [-3])

Write the credit card number backwards and explain why

print(Credit_number [::-1])

Write a script to show the last for like this: xxxx-xxxx-xxxx-4567

Credit_number = “1234 - 5687- 90123 - 4567”

Credit_number = Credit_number[-4:]

print(f”xxxx-xxxx-xxxx-{Credit_number}”)