Make a line edittor that can add lines to a list, save this list to a file file and open a file and read the lines into the list.
It looks like this:
C:\Users\jackie\Desktop>python3 editor.py
> example file
========================================
0: example file
========================================
> with many lines
========================================
0: example file
1: with many lines
========================================
> save a.txt
a.txt saved!
>
^C (Ctrl + C)
C:\Users\jackie\Desktop>python3 editor.py
> open a.txt
========================================
0: example file
1: with many lines
========================================
>
Here are all the components you need:
* read the user input and add it into a list:
lines = []
while True:
a = input("> ")
lines.append(a)
* print list of lines with their line number, and
some header and footer of =====..x40:
print("=" * 40)
for i in range(len(lines)):
print(str(i) + " " + lines[i])
print("=" * 40)
* join list of lines into a string:
lines = ["a","b","c"]
s = "\n".join(lines)
will make the string:
a
b
c
* read the lines of a file:
lines = []
name = "hello.txt"
with open(name, "r") as f:
lines = f.read().splitlines()
* write list of lines to a file:
name = "hello.txt"
with open(name, "w") as f:
f.write("\n".join(lines))
* check if string starts with the word "save"
s = "save hello.txt"
if s.startswith("save "):
print("yes it does")
* split a string into two parts:
s = "save hello.txt"
a,b = s.split(" ")
a is "save"
b is "hello.txt"
Line editors seems silly, but they were the super useful in the 60s and 70s, in fact a lot of the operating systems and laguages back then were written in a line editor called ed, there are three fundamental components to make a computer usefful, assembler - a program that translate instructions into machine code, editor - a program that allows you to write files and a shell a program that allows you to start other programs and interact with them.
The C language was written in ed, the UNIX operating system was written by ed as well.
Add the functionality to delete a line. This is how it should look:
python3 editor2.py
...
> haha amazing
========================================
000: hello
001: this
002: is
003: one
004: line
005: per
006: word
007: haha amazing
========================================
> d 2
========================================
000: hello
001: this
002: one
003: line
004: per
005: word
006: haha amazing
========================================
> d 4
========================================
000: hello
001: this
002: one
003: line
004: word
005: haha amazing
========================================
>
You will need the following:
* how to check if string starts with "d "
if line.startswith("d "):
print("yey")
* how to split a string
line = "d 25"
a,b = line.split(" ")
# a is "d"
# b is "25"
* how to convert string to a number:
x = ["hello","this","is"]
a = "5"
n = int(a)
# access the element at index n from the list x
print(x[n])
* how to delete a item from a list
x = ["hello","this","is"]
# delete the element on index 1
del x[1]
# or you can use pop(1) to
# remove and return the value at index 1
a = x.pop(1)
# or just use x.pop(1) if you dont care about
# the element it is returning
x.pop(1)
* if you try to access a list beyond its size it will
crash, so you need to check if a number fits to be
used as an index
n = 5
if n < len(lines):
print("yey")
Add goto line functionality.
* how to check if string starts with "goto "
if line.startswith("goto "):
print("yey")
* how to split a string
.split(separator) is a method you call on the string
it returns a list splitted by the separator
line = "d 25"
x = line.split(" ")
x is a list ["d","25"]
you can also use destructuring to directly assign
the list into separate variables
a,b = line.split(" ")
a is "d"
b is "25"
* how to convert string to a number:
x = ["hello","this","is"]
a = "5"
n = int(a)
access the element at index n from the list x
print(x[n])
* insert into a list in a specific position
a = ["hello","world"]
x = 1
a.insert(x, "beautiful")
print(a)
prints ['hello', 'beautiful', 'world']
if you try to insert beyond the list size, it will
just add it to the end
x = 20
a.insert(x, "zzz")
print(a)
prints ['hello', 'beautiful', 'world', 'zzz']
* string formatting
python has 'f' strings, which are formatted strings
i = 2
print(f"hello {i:05}")
prints 00002, so it will make sure it will occupy
5 spaces, filling with 0, this is handy if you want
to print things with the same width.
e.g. lets say you have this lines:
0: hello
1: world
...
9: good
10: morning
see how 'morning' is one space to the right, because 10
has one more symbol than 9, so with print(f"{i:02}")
it will look like this:
00: hello
01: world
...
09: good
10: morning
* example code:
x = []
# start at -1, because we always insert on the "next line"
# and in the beginning the next line is going to be 0
# so we need to start at -1
position = -1
while True:
a = input("> ")
if a == "goto 5":
position = 5
else:
# insert at the next line
position += 1
x.insert(position, a)
for line in x:
print(line)
* example how to show which line we have the position on
use f strings in your solution
def printWithLineNumbers(a, position):
print("=" * 40)
for i in range(len(a)):
if i == position:
print("*" + str(i) + ": " + a[i])
else:
print(" " + str(i) + ": " + a[i])
print("=" * 40)
How it should work:
python3 editor2.py
> hello
========================================
*000: hello
========================================
> this is a new
========================================
000: hello
*001: this is a new
========================================
> file
========================================
000: hello
001: this is a new
*002: file
========================================
> with
========================================
000: hello
001: this is a new
002: file
*003: with
========================================
> a lot
========================================
000: hello
001: this is a new
002: file
003: with
*004: a lot
========================================
> of information
========================================
000: hello
001: this is a new
002: file
003: with
004: a lot
*005: of information
========================================
> goto 2
========================================
000: hello
001: this is a new
*002: file
003: with
004: a lot
005: of information
========================================
> that i am writing in my new editor
========================================
000: hello
001: this is a new
002: file
*003: that i am writing in my new editor
004: with
005: a lot
006: of information
========================================
> d 4
========================================
000: hello
001: this is a new
002: file
*003: that i am writing in my new editor
004: a lot
005: of information
========================================
> which is amazing and it can edit
========================================
000: hello
001: this is a new
002: file
003: that i am writing in my new editor
*004: which is amazing and it can edit
005: a lot
006: of information
========================================
> goto 6
========================================
000: hello
001: this is a new
002: file
003: that i am writing in my new editor
004: which is amazing and it can edit
005: a lot
*006: of information
========================================
> now i will append in the end of the file
========================================
000: hello
001: this is a new
002: file
003: that i am writing in my new editor
004: which is amazing and it can edit
005: a lot
006: of information
*007: now i will append in the end of the file
========================================
>
She was super tired after shool and training, so I had to help out a lot.
Make goto support goto 7 to go to specific line index, and goto hello to go to the first line that contains the word hello
* check if a string is an integer:
z = "helloo"
if z.isdigit():
print("Z IS A DIGIT")
else:
print("Z IS NOT A DIGIT")
* find the first line containing a string
def find(where, what):
for i in range(len(where)):
if what in where[i]:
return i
return -1
x = ['hello world', 'b' ,'hello']
found = find(x, "b")
if found >= 0:
print(f"index {found} matching with value {x[found]}")
How it should look:
> hello
========================================
*000: hello
========================================
> world
========================================
000: hello
*001: world
========================================
> this is hello
========================================
000: hello
001: world
*002: this is hello
========================================
> how can it be
========================================
000: hello
001: world
002: this is hello
*003: how can it be
========================================
> blabla
========================================
000: hello
001: world
002: this is hello
003: how can it be
*004: blabla
========================================
> goto world
========================================
000: hello
*001: world
002: this is hello
003: how can it be
004: blabla
========================================
> goto 3
========================================
000: hello
001: world
002: this is hello
*003: how can it be
004: blabla
========================================
> z
========================================
000: hello
001: world
002: this is hello
003: how can it be
*004: z
005: blabla
========================================
> goto world
========================================
000: hello
*001: world
002: this is hello
003: how can it be
004: z
005: blabla
========================================
> m
========================================
000: hello
001: world
*002: m
003: this is hello
004: how can it be
005: z
006: blabla
========================================
>
Lookup the documentation for .split(" "), to see how to make "goto hello world" be split into ["goto", "hello world"] instead of ["goto","hello","world"] (hint, .split() takes two parameters, separator which in our case is " ", and maxsplit, which by default is -1, but you can limit how many times you want to split)
today was a 'write this code and lets go over it' kind of lesson
When adding a line, use the number of starting spaces from previous line this is super handy if you are writing python, or a presentation.
This is how it should look:
> hello
========================================
*000: hello
========================================
> testing
========================================
000: hello
*001: testing
========================================
> another line
========================================
000: hello
001: testing
*002: another line
========================================
>
========================================
000: hello
001: testing
002: another line
*003:
========================================
> and again
========================================
000: hello
001: testing
002: another line
003:
*004: and again
========================================
> goto 2
========================================
000: hello
001: testing
*002: another line
003:
004: and again
========================================
> zzz
========================================
000: hello
001: testing
002: another line
*003: zzz
004:
005: and again
========================================
>
use the following function which just iterates the characters of a string and counts spaces and breaks out if it sees the first non space
def countSpaces(string):
n = 0
for character in string:
if character == ' ':
n += 1
else:
break
return n
you need to use this function to modify the 'line' if we have a previous line and the current line has at least 1 character:
while True:
line = input('> ')
...
else:
if pos >= 0 and pos < len(lines) and len(line) > 0:
prev = lines[pos]
prefix = (' ' * countSpaces(prev)) # n spaces
line = prefix + line
Create 1000 files 1.txt 2.txt etc.. each file should contain "hello\n" 500 times
MAKE BIG STRING:
# make a string containing "hello\n" 500 times:
a = "hello\n" * 500
WRITE TO A FILE:
# with open and close
name = "1.txt"
f = open(name, "w")
s = "hello\n"
f.write(s)
f.close()
# or using `with` so it automatically closes the file:
name = "1.txt"
s = "hello\n"
with open(name, "w") as f:
f.write(s)
We made a small test:
# insert 100000 random integers between 1 and 1000 in a list
# find the smallest number
# find the largest number
def find_smallest(x):
n = 0
# ...
# code that finds the smallest
return n
def find_largest(x):
n = 0
# ...
# code that finds the largest
return n
import random
numbers = []
for i in range(100000):
# append random numbers between 1 and 1000 to the list
smallest = find_smallest(numbers)
largest = find_largest(numbers)
print(f"smallest: {smallest}, largest: {largest}")
After the test is done, google for 'how to find smallest/largest numbers from a ist in python' and see how the min and max functions work.