Conditionals with Strings

Problem Check-list

• bouncer
• targets
• word_finder
• mixed_case
• dictionary_corner
• number_sort
• palindrome
• substring

Useful String Conditions

Equals and inequalities

We can test whether strings are equal just like integers using ==.

If we want to test whether strings would be before or after each other in the dictionary, we can use >, >=, < and <=:

	if "Apple" < "Banana":
		print("Apple is before Banana")

However, be careful because case is important here. If we try:

	if "apple" > "Banana":
		print("apple is after Banana")

This will print "apple is after Banana". This is because strings are case sensitive and the lower-case alphabet comes after the upper case alphabet.

Case

To change the case of a string, we can use the methods::

• "My stRiNg".upper() # "MY STRING"
• "My stRiNg".lower() # "my string"
• "My stRiNg".title() # "My String"
• "My stRiNg".capitalalize() #"My string"

This is useful to, amongst other things, check whether two strings are the same without worrying about case:

	if "Apple".lower() == "aPPLe".lower():
		print("Same word, potentially different case")

We can also check the case of a word using the methods:

• "my string".isupper() # False
• "my string".islower() # True
• "My String".istitle() # True

	if "my string".islower():
		print("That's a lowercase string!")

String length

We can find the length of a string (the number of characters, including spaces), easily by using the len function:

	s = "A string with many words!"
	if len(s) > 10:
		print("That's a long word!")

Characters and substrings

Splicing a string into its constituent characters and substrings is easily achieved using square brackets and operates much like the range object for numbers. Remember that counting starts at 0 here.

	s = "My example string"
	#	 01234567890123456   - The character numbers (the second 0 = 10 and so on)

	print(s[0])					# M - the first character.
	print(s[4])					# x - the 5th character
	print(s[-2])				# n - the second last character

	print(s[3:7])				# exam - characters 3 to 6
	print(s[11:])				# string - character 11 onwards
	print(s[:10])				# My example - characters up to character 9.
	
	print(s[0:10:2])			# 'M xml' - every second character from 0 to 9
	print(s[::-1])				# 'gnirts selpmaxe yM' - all characters in reverse order

Checking for prefixes/suffixes/substrings

If we would like to check whether a string starts or finishes with a particular character or substring, we can use the methods:

* `"My string".startswith("My")		# True`
* `"My string".endswith("ring")		# True`

The keyword in will also allow us to check for substrings:

	s = "My example string"
	if "exam" in s:
		print("Found 'exam' in the string")