Week 8 - text (strings) & data from CSV files

Question 1

How to use the index operator with strings?

Answer 1

[] used to index a character. Each character is a unique index.
Starts at 0
-1 looks to the last character in the string.

Question 2

What does a dot.notation combine

Answer 2

objects with methods.

example - object.method()

Question 3

How to use the slice operator with strings?

Answer 3

[n:m] - returns part of a string from the nth character to the mth character. However excludes the mth character (stops at the one before).

Question 4

What do the “in” and “not in” operators do?

Answer 4

‘in’ tests if one string is a subset of another string

‘not in’ returns the logic opposite to ‘in’

Question 5

What string operators also work for lists too?

Answer 5

indexing
slicing
searching (in and not in)
looping
concatenating

Question 6

How to open a file in python?

Answer 6

open file = open(file_path, mode)
modes:
'r' = reading a text file
'rb' = reading a binary file
'w' = writing a text file
'wb' writing a binary file

Question 7

What methods are used to read a file?

Answer 7

variable_name.readlines(file_variable) - reads all the lines into a list
variable_name.read(file_variable) - reads whole file into one big string.

Question 8

How to read CSV files

Answer 8

import CSV - python module that helps read compex csv files.
variable_name = csv.reader(file)

Question 9

How to use the CSV dictionary reader?

Answer 9

csv.DictReader() converts each row into a dictionary with the column header as the key.

Question 10

How do you count using a looping program?

Answer 10

This counts a sequence of values

1. Initialise a counter variable with zero before the loop
2. Increment the counter in the loop (i.e. count = count + 1)

Question 11

How do you sum using a looping program?

Answer 11

Sums a sequence of values

1. Initialise a sum variable with zero before the loop.
2. Add the value to the sum variable each time it loops (i.e. salary = salary + float(loop_variable[“key”])

Question 12

How do you average using a looping program?

Answer 12

1. Combine the count and sum programs

2. Then print(sum/count)

Question 13

How do you accumulate data through a looping program?

Answer 13

Save the data to a list []
1. Initiate a variable with a blank list []
2. choose a particular colum:
a. create a variable that selects the key (top of the
program.)
b. create a variable inside the loop that selects
only the key (i.e. value = Ist_col[key]
3. Append key to list (ie. blank_list_variable.append(key_variable)