Strings are bits of text. They can be defined as anything between quotes:
astring = "Hello world!"
As you can see, the first thing you learned was printing a simple sentence. This sentence was stored by Python as a string. However, instead of immediately printing strings out, we will explore the various things you can do to them.
print len(astring)
That prints out 12, because "Hello world!" is 12 characters long, including punctuation and spaces.
print astring.index("o")
That prints out 4, because the location of the first occurrence of the letter "o" is 4 characters away from the first character. Notice how there are actually two o's in the phrase - this method only recognizes the first.
But why didn't it print out 5? Isn't "o" the fifth character in the string? To make things more simple, Python (and most other programming languages) start things at 0 instead of 1. So the index of "o" is 4.
print astring.count("l")
For those of you using silly fonts, that is a lowercase L, not a number one. This counts the number of l's in the string. Therefore, it should print 3.
print astring[3:7]
This prints a slice of the string, starting at index 3, and ending at index 6. But why 6 and not 7? Again, most programming languages do this - it makes doing math inside those brackets easier.
If you just have one number in the brackets, it will give you the single character at that index. If you leave out the first number but keep the colon, it will give you a slice from the start to the number you left in. If you leave out the second number, if will give you a slice from the first number to the end.
You can even put negative numbers inside the brackets. They are an easy way of starting at the end of the string instead of the beginning. This way, -3 means "3rd character from the end".
print astring.upper()
print astring.lower()
These make a new string with all letters converted to uppercase and lowercase, respectively.
print astring.startswith("Hello")
print astring.endswith("asdfasdfasdf")
This is used to determine whether the string starts with something or ends with something, respectively. The first one will print True, as the string starts with "Hello". The second one will print False, as the string certainly does not end with "asdfasdfasdf".
afewwords = astring.split(" ")
This splits the string into a bunch of strings grouped together in a list. Since this example splits at a space, the first item in the list will be "Hello", and the second will be "world!".
Try to fix the code to print out the correct information by changing the string.
s = "Hey there! what should this string be?"
# Length should be 20
print "Length of s = %d" % len(s)
# First occurrence of "a" should be at index 8
print "The first occurrence of the letter a = %d" % s.index("a")
# Number of a's should be 2
print "a occurs %d times" % s.count("a")
# Slicing the string into bits
print "The first five characters are '%s'" % s[:5] # Start to 5
print "The next five characters are '%s'" % s[5:10] # 5 to 10
print "The twelfth character is '%s'" % s[12] # Just number 12
print "The last five characters are '%s'" % s[-5:] # 5th-from-last to end
# Convert everything to uppercase
print "String in uppercase: %s" % s.upper()
# Convert everything to lowercase
print "String in lowercase: %s" % s.lower()
# Check how a string starts
if s.startswith("Str"):
print "String starts with 'Str'. Good!"
# Check how a string ends
if s.endswith("ome!"):
print "String ends with 'ome!'. Good!"
# Split the string into three separate strings,
# each containing only a word
print "Split the words of the string: %s" % s.split(" ")
Length of s = 20
The first occurrence of the letter a = 8
a occurs 2 times
The first five characters are 'Strin'
The next five characters are 'gs ar'
The twelfth character is 'a'
The last five characters are 'some!'
String in uppercase: STRINGS ARE AWESOME!
String in lowercase: strings are awesome!
String starts with 'Str'. Good!
String ends with 'ome!'. Good!
Split the words of the string: ['Strings', 'are', 'awesome!']