range() and enumerate()

The usual way to iterate over a range of numbers or a list in python, is to use range().

Example 0:

[code language="python"] colors = ["yellow", "red", "blue", "white", "black"]

for i in range(len(colors)): print(i, colors[i]) [/code]

This should output:

[code language="bash"] (0, 'yellow') (1, 'red') (2, 'blue') (3, 'white') (4, 'black') [/code]

print(), by default, returns a tuple. If we want to print it in a more presentable way, we’ll need to find the indice at which each value is, and print that as well. Re-write the code a bit, to achieve the desired output:

[code language="python"] colors = ["yellow", "red", "blue", "white", "black"]

for i in range(len(colors)): color = colors[i] print("%d: %s" % (i, color)) [/code]

This should print:

[code language="bash"] 0: yellow 1: red 2: blue 3: white 4: black [/code]

We can see that the above output starts with ‘0’ since python starts counting from ‘0’. To change that to ‘1’, we’ll need to tweak the print() statement.

[code language="python"] colors = ["yellow", "red", "blue", "white", "black"]

for i in range(len(colors)): color = colors[i] print("%d: %s" % (i + 1, color)) [/code]

This should print:

[code language="bash"] 1: yellow 2: red 3: blue 4: white 5: black [/code]

Even though the above code snippet isn’t that complex, a much better way exists to do this. This is where the builtin function enumerate() comes in.

enumerate() returns a tuple when passed an object which supports iteration, for example, a list. It also supports a second argument named 'start' which default to 0, and can be changed depending on where to start the order. We’ll check what 'start' is towards the end of this article.

[code language="python"] colors = ["yellow", "red", "blue", "white", "black"] print(list(enumerate(colors))) [/code]

This returns a list of a tuples.

[code language="bash"] [(0, 'yellow'), (1, 'red'), (2, 'blue'), (3, 'white'), (4, 'black')] [/code]

To get to what we desire, modify it as:

[code language="python"] for i, color in enumerate(colors): print('%d: %s' % (i, color)) [/code]

This outputs:

[code language="bash"] 0: yellow 1: red 2: blue 3: white 4: black [/code]

Remember that we talked about that enumerate() takes a second value named 'start' which defaults to ‘0’? Let’s check how that’ll help here.

The above output starts with ‘0’. 'start' can help to change that.

[code language="python"] for i, color in enumerate(colors, start=1): print('%d: %s' % (i, color)) [/code]

This should change the output as:

[code language="bash"] 1: yellow 2: red 3: blue 4: white 5: black [/code]