Solutions

A range of possiblities

In [12]:
print(list( range(0, 10, 1) ))

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

This does exactly what our first range command did, we have just explicitly specified the default values, start=0 and step=1.

In [13]:
print(list( range(0, 10, 2) ))

[0, 2, 4, 6, 8]

This steps through the even integers, because we have changed the value of step from the default 1 to 2.

In [14]:
print(list( range(10, 0) ))

[]

This returns an empty list because there are no numbers starting at 10 that are smaller than 0.

In [15]:
print(list( range(10, 0, -2) ))

[10, 8, 6, 4, 2]

Because of step=-2, the order of the range is reversed and so it produces the list of numbers greater than stop.

In [16]:
print(list( range(1, 2, 0.1) ))

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-16-1be1b2d16426> in <module>
----> 1 print(list( range(1, 2, 0.1) ))
TypeError: 'float' object cannot be interpreted as an integer

range takes only integer values so this raises a TypeError: 'float' object cannot be interpreted as an integer.

Looping over a list

In the first example of a loop we assigned a list to numbers and used this as the collection of values to loop over - we can do exactly the same here. We can avoid using len by looping over the values in pressures, but we still need a variable num_pressures to count the number of pressures we summed up, and sum_pressures to record the running total:

In [18]:
pressures = [0.273, 0.275, 0.277, 0.275, 0.276]
sum_pressures = 0.0
num_pressures = 0
for p in pressures: #for each value p in the list pressures
    sum_pressures += p #add the value of p to the current total
    num_pressures += 1 #add one to the number of values we have added up
mean_pressure = sum_pressures / num_pressures
print("The mean pressure is:", mean_pressure)

The mean pressure is: 0.2752

Generally this would be considered more "pythonic" than the previous example, because it is more readable. 'For each index in a range the length of the list pressures ...' is not as readable as 'For each pressure in the list of pressures ...'. We have also introduced the accumulator operator += in the line

value += new_value

This is the same as writing value = value + new_value but is shorter and easier to read. There is also a "deccumulator" (that's not an official name) operator -= which does what you expect;

value -= new_value

is the same as

value = value - new_value

Looping over a string

We can use the same idea as before, remember to read Python's for loop syntax as

for item in my_list:
In [19]:
for character in "Hello world!":
    print(character)

H
e
l
l
o
w
o
r
l
d
!