Chapter 11 (files)

Question 1

How do you access the contents of a file?

Answer 1

variable = open(‘file name’, ‘designator’)
designator tells the program how it uses the file
or
with open() as variable:
—- indented code
file will automatically closed after the indented code is finished

Question 2

How do you read the contents in the file?

Answer 2

variable1 = open(‘file.txt’)
variable2 = variable1.read()

Question 3

What is a file extension?

Answer 3

.pdf .txt .doc etc.
Hints to the computer how the contents of the file should be organized

Question 4

What file designator allows you to append to a file?

Answer 4

‘a’

Question 5

What file desginator allows you to read a file?

Answer 5

‘r’

Question 6

What file designator allows you to write to a file?

Answer 6

‘w’

Question 7

What file designator allows you to read and write to a file?

Answer 7

‘r+’

Question 8

What are the file designators?

Answer 8

r = reading
w = writing to a new file or overwrite an existing file
a = appending (adding data)
rb/rw/ra = read/write/append binary data
r+ = read and write to the file
rb+ = read, write and binary file

Question 9

How do you close a file?

Answer 9

variable.close()

Question 10

How do you write into a file?

Answer 10

fileID.write(‘string’)
- or use string variable as a parameter

Question 11

How do you search for a file for your code?

Answer 11

fileID = open(‘location1//location2//file.txt’,’designator’)

Question 12

How do you loop through each line of a file?

Answer 12

for line_num in fileID:
—- indented code

Question 13

How to put individual lines of a file into a list?

Answer 13

list1 = fileID.readlines()
or
list2 = list(fileID)

Question 14

How do you read a certain number of bytes?

Answer 14

fileID.read(no.bytes)

Question 15

Why is there a delay when using the write() command to a file?

Answer 15

There is a buffer before the text is written to the file, it is stored in memory then pasted into the file after a new line is written: write(‘\n’)

Question 16

How do you remove the buffer from writing to a file?

Answer 16

fileID = open(‘file_name’,’w’,buffering = 0)

Question 17

How do you set a specific number of bytes to buffer when using the write() command?

Answer 17

fileID = open(‘file_name’, ‘w’, buffering = x)
- x represents the number of bytes

Question 18

How do you forcibly write buffered text into a file?

Answer 18

fileID.flush()
or
os.fsync(fileID)

Question 19

What does the ‘with’ statement do?

Answer 19

opens a file, has indented code, then forcibly closes the file after the indented code has run

Question 20

How do you split a string?

Answer 20

list = string.split(‘char’)
the split statement removes the character from the string when splitting

Question 21

What does an empty .split() statement do

Answer 21

Split a string by white spaces including new lines

Question 22

What does .split(‘\n’) do?

Answer 22

Splits the string at a new line, if there is no string after the new line then the data stored in the last index of the new list is empty ‘’

Question 23

What does .join() do?

Answer 23

The inverse of split, it takes the data in a list and joins them together with some kind of separator
list1 = [‘hello’, ‘its’, ‘me’]
separator = ‘/’
string = separator.join(list1)
output = hello/its/me

Question 24

What is a csv?

Answer 24

comma separated values, instead of separating data into rows and columns the rows are separated by commas (each row is one string)
- A piece of data between the commas in a csv are called fields

Question 25

How do you read row by row from a csv file?

Answer 25

import csv
with open(‘file.csv’,’r’) as csv_file:
reader = csv.reader(csv_file)
for row in reader:
print(row)
- This will print each row of data from the csv file
- by default csv.reader reads the fields between the commas, if there is a different separator then you can add a delimiter to change what the csv.reader uses to separate fields:
reader = csv.reader(csv_file, delimiter = ‘;’)

Question 26

Can you write to a csv file?

Answer 26

Yes, when you call the file just use ‘w’ as the delegator

Question 27

How do you write each element of a list to each line of a file?

Answer 27

fileID.writelines(list)
- list must be a string