ord('a') 
# Return the Unicode code point for a one-character string. 
# Returns 97
chr(97) 
# Return a Unicode string of one character with ordinal i 
# Returns 'a'

greet = "Hello Bob"
print(greet[0])

print(greet[0], greet[2], greet[4])

x = 8
print(greet[x - 2])

print(greet[-1])
print(greet[-3])
print(greet[50]) # Error

print(greet[-(len(greet)+1)]) # This throws an error,  
# it implies a character before the start of the string

# You can concatenate strings together
s = "Lets" + "add" + "together" + "strings"
print(s) # Note is just puts them one after the other 
# (i.e. it doesn't do any whitesppace addition)

s = "Hello" * 10 
# The multiplication operator allows you to 
# make a sequence of strings
print(s) 

# Note this doesn't work
# What would this even do?
s = "You can't" - "subtract strings" 
# Nor does this
s = "You can't" / "divide strings either"

s = "A long string"
print(len(s))
# The empty string case
s = "" 
print(len(s))
# A String with whitespace character
s = "\t"
print(len(s))

s = "A long string"

# Realise that a character is just another string in Python
# In some languages, like C/C++, individual characters 
# are not strings but have a different type, but Python 
# treats them as a single character string

print(type(s[0])) # Prints str
print(len(s[0])) # Prints 1

# Beyond indexing, you can slice strings to create substrings

greet = "Hello Bob"

print(greet[0:3]) # The 'prefix' substring of the first 3 characters

print(greet[3:3]) # The interval [3, 3) is empty

print(greet[5:8])

# Negative length strings?
print(greet[6:0]) # If the second index occurs before the first index it won't
# throw an error, just make a zero length (empty) string

print(greet[:5]) # This is the same as greet[0:5]
# greet[:n] is called a prefix of greet, where n is in [0, len(greet))

print(greet[5:]) # This is the same as greet[5:9]
# greet[n:] is called a suffix of greet, where n is in [0, len(greet))

print(greet[:]) # This is just the whole string, allowing you to make
# a copy of the string

s = "Strings can't be changed"

# This doesn't work

s[0] = 's'

# To make s lower case you could instead do:

s = 's' + s[1:]

print(s)