Exercises in .NET with Andras Nemes

Python language basics 37: splitting a delimited string

Introduction

In the previous post we saw how to efficiently concatenate strings using the join function. We showed a little trick to build one string from several others with a space in between.

In this post we’ll quickly look at the exact opposite, i.e. how to split a delimited string.

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Python language basics 36: string concatenation using the join method

Introduction

In the previous post we discussed how to use the ‘in’ operator to determine whether a certain element is found in a collection. You can apply this operator – and its negation ‘not in’ – on all collection types including strings.

In this post we’ll look at a useful String function called ‘join’ to concatenate bits of strings into a single one.

String concatenation

Basic string concatenation is performed using the addition operator ‘+’:

combined = "Welcome" + " to" + " my blog " + "dear " + "readers"
print(combined)

‘combined’ will become “Welcome to my blog dear readers” as expected. Do you recall that strings are immutable in Python – and in fact all major programming languages? The problem with the above statement is that it creates multiple strings in succession as the ‘+’ operator is applied:

Welcome
to
Welcome to
my blog
Welcome to my blog

etc.

‘combined’ will at the end point at the string “Welcome to my blog dear readers” in memory. The other values will be kept in memory until the garbage collector cleans them up as unused resources without references.

A more efficient solution is the join function although its usage is a bit strange at first sight. It operates directly on a string which will become a string delimiter. Here’s an example:

combined = '|'.join(("This", "is", "a", "delimited", "string"))
print(combined)

combined will become:

This|is|a|delimited|string

Can you guess why we needed 2 pairs of parenthesis? The inner pair is the way to declare the tuple collection which we discussed in this post. The join method takes only one argument and it must be a collection. Hence we need to wrap the strings to be concatenated in a collection. A string list works equally well:

combined = '|'.join(["This", "is", "a", "delimited", "string"])
print(combined)

‘combined’ will be the same as above.

How can we build the same “Welcome to my blog dear readers” like above? What is the delimiter here? It’s of course the space character ‘ ‘:

combined = ' '.join(["Welcome", "to", "my", "blog", "dear", "readers"])
print(combined)

‘combined’ will evaluate to “Welcome to my blog dear readers” as it was intended.

Read the next part here.

Read all Python-related posts on this blog here.

Python language basics 35: determine if an element is included in a collection

Introduction

In the previous post we looked at how to return multiple values from a function in Python. We saw that this is fact was only possible through a trick where the trick was to use a collection of type Tuple. We went through an example with a simple function that returned 4 values in a tuple. We also discussed how to access individual elements in the tuple.

In this post we’ll see how to determine if a certain element is located in a collection.

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Python language basics 34: returning multiple values from a function

Introduction

In the previous post we looked at the idea of local and global variables. We saw how a variable with function-level focus could shadow another variable with the same name but global scope. Finally we discussed how to indicate our intention to use the global level variable using the “global” keyword.

In this post we’ll look at a technique to return multiple values from the same function.

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