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l = [1,4.5, 6, 9.0, 10, -1]
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l
The most basic operation on a list is extracting its elements at a given position.
For that we use the position in the list keeping in mind that the first element starts at 0.
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l[0]
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l[5]
The indexing also works backwards using negative numbers
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l[-1]
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l[-3]
If you try to use an index beyond the list size you will get an error
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l[6]
Lists are mutable. That means you can change the value of an item as follows
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l[0] = 100
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l
Arguably, the most useful list operation is slicing.
You can use it to quickly select a subset from the list.
Slicing consists in using two different indices separated by : to select the elements
with the syntax l[start:end]
Here are some examples. Please be sure that you understand how tthe start:end indexing works!. That's the whole point of slicing, if some of the examples are unclear, please ask!
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print(l) # this is the full list
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l[0:4] #start=0, end=4
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l[2:4] #start=2, end=4
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l[-4:-1] #start=-4, end=-1, negative values are allowed.
Slicing also works if you use only one index.
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l[3:]
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l[:4]
The mathematical operations + and * can also be used with lists.
The first operation is used for concatenation and the second for repetition.
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m = [45, -56]
print('l=', l)
print('m=', m)
n = l + m
print('n=',n) # this is the concatenation
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m + l #sum of lists does not commute!
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2 * l # here I am reapeating the list `l` two times.
The function sorted can be used on lists to reorder the objects
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l_sorted = sorted(l)
print(l_sorted)
and the function len gives you the number of items in the list
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len(l)
In python the strings are defined as a list of characters
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given_name = "Silvia"
family_name = "Rivera Cusicanqui"
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print(given_name + " " + family_name) # This is the concatenations of the strings
These strings have many useful methods
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given_name.upper() #convert to upper case
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given_name.replace('i', 'y') #replace 'i' with 'y'
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given_name.count('i') # count how many times 'i' is the string
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family_name.split() # split the original string in the places with spaces, the result is a new list.
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