Helpful examples

These should come in handy when completing the assignment.

Test reading a `csv`-file

make a folder in the notebooks-directory called: assignment
copy the csv-file containing your family's birth dates into it



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# assign the path to the csv-file to the variable 'path_to_csv'
path_to_csv = 'assignment/birth.csv'



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# open the csv-file for reading
# fp is a "file pointer" to the data payload of the file (text)
fp = open(path_to_csv, 'r')



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# read the contents of the file into a new variable, 
file_cont = fp.read()

# REMEMBER TO CLOSE the file (more critical when writing)
fp.close()



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# see what we got
file_cont



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type(file_cont)

Read file line-by-line



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fp = open(path_to_csv, 'r')

Exute the following cell repeatedly until you no longer get anything out of the file (Control-Enter will be useful)



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line = fp.readline()
print(line)



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fp.close()

Read the file into a list of lines



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fp = open(path_to_csv, 'r')
all_lines = fp.readlines()
fp.close()



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type(all_lines)



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all_lines  # show them



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type(all_lines[1])  # what type is the 2nd element of the list?



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all_lines[1]  # hi Dad!

Split a string at a character

Let's make a list of all birth dates. For this, we want to

loop over all lines, starting from the 2nd line (1st is the column names)
split each line on the comma (,)
- this creates a list of length 3 for name, date and place
print the 2nd element of the split-list



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# test the split-method
all_lines[1].split(',')



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# loop from the 2nd element, to the end
# use the 'slice'-notation [1:], meaning "from index 1 to end"
for li in all_lines[1:]:
    split_line = li.split(',')
    print(split_line[1])

Strings can be sliced: they're lists of characters

Repeat the above, but now only print the third and fourth digits of the birth year!



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for li in all_lines[1:]:
    split_line = li.split(',')
    print(split_line[1][2:])  # NB: [1][2:]

Since split_line[1] is a string, split_line[1][2:] reads:

show the characters from the third element of the string split_line[1] to the end

Lists can be appended to

Starting with a list of values, add a new item (to the end) using the .append-method:



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my_list = ['apple', 'orange']
print('My list is', len(my_list), 'elements long.')

my_list.append('banana')
print('My list is', len(my_list), 'elements long.')
print(my_list)

Often it's useful to start with an empty list and append to it:



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new_list = []  # an empty list: nothing between the hard brackets
print('Before append:', new_list)
new_list.append(42)
print('After append:', new_list)

Is `x` in a list? Use the `in`-operator

In Python, we have a handy boolean operator for finding out whether an item exists in a list:



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print(my_list)  # ['apple', 'orange', 'banana']
print('orange' in my_list)
print('kiwi' in my_list)
print('Orange' in my_list)  # case-sensitive!