Part 3.4Strings in Python

Strings are sets of ordered characters that make up text. Strings are normally contained within " " or ' '.

String tools

Strings can be manipulated in many different ways such as with other programming languages such as Java. For instance, the substring method will get a smaller inner string from within a string (a substring). In PHP, there are several generic string methods.

Replace a string inside a string

String replacement is an often used in Python for replacing some substring within another string. In Python, this is a chained function applied to a value:

myStr = "Hello everyone!"
myStr = myStr.replace("everyone", "world")
print (myStr)
    

Get the length of a string

As strings are arrays of characters, it is possible to get the length of a string using the len method:

myStr = "Hello everyone!"
print (len(myStr))
    

Getting the index of the first occurence of a string

Python also provides a find method that can be applied to strings. This method will return an integer that represents the index of the first character of a substring within another string.

myStr = "Hello everyone!"
print (myStr.find("Hello"))
print (myStr.find("everyone"))
    

Getting a substring from a string

The word substring has been used throughout this article. It's meaning is a string that is within another string. For instance, "everyone" is within the string "Hello everyone!". The same can be said for "Hello" but not for "hello". This is because substrings are case sensitive.

Python's syntax is different to many other languages in the fact it does not have a substring method. Instead, Python relies on the index of a string using an interesting syntax:

myStr = "Hello everyone!"
print (myStr[6:11])
print (myStr[:5])
print (myStr[6:])
    

The [5:7] following a number means from character 5 to 7 (remembering that Python counts from 0 upwards, not 1). The [:6] index means from the start to 6. The [6:] index means from 6 to the end of the string.

Concatenating two strings

String concatenation is the joining of two or more strings. Python uses the + operator for concatenation:

myStr1 = "Hello "
myStr2 = "world"
concatenated = myStr1 + myStr2
print (concatenated)
    

Getting a character from a string position

Getting a character from a string in Python is achieved with the same method as getting a substring by using the index of the character:

myStr = "Hello everyone!"
print (myStr[4])
    

The above sample will return the 5th character of the string.

Using quotes inside a string

It is already obvious that since strings in Python can be within a double quote " or a single quote ' that they can be interchanged to include a single or double quote within the output. For example:

print ("Jamie's Code")
print ('"' + "Jamie's Code" + '"')
    

But there is an easier way to do this called escaping. Escaping is done with the backslash character \ in front of the character to be escaped:

print ('"Jamie\'s Code"')
print ("\"Jamie's Code\"")
    

This is such a useful technique that saves both writing time and compile time.