Make An Terminal Editor In Python
Make a line editor in Python
Most programmers have wondered how to write an editor. Most elect to use Tk, if they use Python.
However, today, I will document how I created my editor, JEDI.
JEDI is a line editor. (If you are a Vi[m] user, think ‘:’)
The starter command set:
a: (a)ppend to file
e: (e)dit file
w: (w)rite to file
q: (q)uit
Now, let’s start programming!
These instructions are written for GNU+Linux. (Darwin/macOS may work)
cd ~
mkdir Python/jedi
python3 -m venv env
source env/bin/activate
git init
That sets up our working directory.
Let’s edit editor.py
class editor:
def __init__(self, filename):
self.source = open(filename, 'r').read().split('\n')
def read(self):
print(self.source)
That big block of text in line 3 is my prefrred way of reading a file, and splitting it by line. open(filename, ‘r’): Make a file object pointing to filename in read mode read(): read the contents of the file as a string split(‘\n’): Split the string into an list, using \n as the delimiter
And now for main.py
from editor import editor
e = editor('main.py')
e.read()
Expected output:
['from editor import editor', "e = editor('main.py')", 'e.read()']
We are now going to impliment the io for adding, opening, and writing.
editor.py should now look like this:
class editor:
def __init__(self, filename=""):
self.fd = filename
if self.fd!="" : # Not ""
self.source = self.read(filename)
else:
self.source = []
def read(self, fn):
return open(fn, 'r').read().split('\n')
def append(self, arr):
assert type(arr) is list
for item in arr:
self.source.append(item)
def write(self):
f = open(self.fd, 'w')
payload = ""
for item in self.source:
payload += (item + '\n')
f.write(payload)
f.close()
And main.py should look like this:
from editor import editor
import sys
prompt = '*'
e = editor(sys.argv[1])
while True:
command = input(prompt) # TODO: Make prompt with -p
if command == 'a':
data = []
txt = ""
while txt != "`":
txt = input()
data.append(txt)
e.append(data)
elif command == 'w':
e.write()
elif command == 'q':
break
Now, let’s clean up the UI a bit, using argparse. Add these changes to main.py:
from editor import editor
import argparse <=
# Create the parser
parser= argparse.ArgumentParser(description='JEDI is a Ed clone, made in the 21st Century') <=
# Add the arguments
parser.add_argument('file', type=str, help='The path used to access the file to edit (Ex: ~/.bashrc') <=
parser.add_argument('-p', action='store', type=str, help='The prompt string to be used') <=
args = parser.parse_args() <=
e = editor(args.file) <=
while True:
command = input(args.p) <=
if command == 'a':
data = []
txt = ""
while txt != "`":
txt = input()
data.append(txt)
e.append(data)
elif command == 'w':
e.write()
elif command == 'q':
break
Now we can add to a file, but we cannot
- See the file
- Goto a line
We need to add more commands to editor.py
class editor: def __init__(self, filename=""): self.fd = filename self.cursor = 0 if self.fd!="" : # Not "" self.source = self.read(filename,caller=1) else: self.source = [] print(self.source) def read(self, fn, caller=0): try: return open(fn, 'r').read().split('\n') except FileNotFoundError: if caller == 1: print("No such file or directory") else: return 1 def append(self, arr): for item in arr: self.source.insert(self.cursor, item) self.cursor +=1 def write(self): f = open(self.fd, 'w') payload = "" for item in self.source: payload += (item + '\n') f.write(payload) f.close() #============== Add all text after this ================= def getline(self, lineno): if lineno <= len(self.source): return self.source[lineno] else: return 1 def goto(self, pos): pos = int(pos) if pos <= len(self.source): self.cursor = pos return 0 else: return 1 def isint(self, test): try: int(test) return True except ValueError: return False def getln(self, loc="NAN"): if loc == "NAN": loc = self.cursor return self.source[loc] def getpos(self): return self.cursor def getlen(self): return len(self.source)And add this to main.py: ```python3 from editor import editor import argparse
Create the parserr
parser= argparse.ArgumentParser(description=’JEDI is a Ed clone, made in the 21st Century’)
Add the arguments
parser.add_argument(‘file’, type=str, help=’The path used to access the file to edit (Ex: ~/.bashrc’) parser.add_argument(‘-p’, nargs=’?’, const=’’, action=’store’, type=str, help=’The prompt string to be used’) def split(word): return [char for char in word] args = parser.parse_args()
e = editor(args.file) p = args.p if p == ‘None’: p=’’ while True: command = split(input(p)) if command[0] == ‘a’: data = [] txt = “” while txt != “`”: data.append(txt) txt = input() data.remove(data[0]) e.append(data) elif command[0] == ‘w’: e.write() #=========== Add from here =========== elif e.isint(command[0]): e.goto(command[0]) elif command[0] == ‘p’: if len(command) == 1: print( e.getln()) elif len(split(command)) == 2: print(e.getln(int(command[1]))) #=========== To Here =========== elif command[0] == ‘q’: break
The new command set: p: (p)rint a line (Ex: p15) (any int): Goto line a: (a)ppend to file e: (e)dit file w: (w)rite to file q: (q)uit
We are now goting to add the final command needed for a basic editor: Delete
```editor.py```
```python3
class editor:
def __init__(self, filename=""):
self.fd = filename
self.cursor = 0
if self.fd!="" : # Not ""
self.source = self.read(filename,caller=1)
else:
self.source = []
def read(self, fn, caller=0):
try:
return open(fn, 'r').read().split('\n')
except FileNotFoundError:
if caller == 1:
print("No such file or directory")
else:
return 1
def append(self, arr):
for item in arr:
self.source.insert(self.cursor, item)
self.cursor +=1
def write(self):
f = open(self.fd, 'w')
payload = ""
for item in self.source:
payload += (item + '\n')
f.write(payload)
f.close()
def getline(self, lineno):
if lineno <= len(self.source):
return self.source[lineno]
else:
return 1
def goto(self, pos):
if not isint(pos):
return 1
pos = int(pos)
if pos <= len(self.source):
self.cursor = pos
return 0
else:
return 1
def isint(self, test):
try:
int(test)
return True
except ValueError:
return False
def getln(self, loc="NAN"):
if loc == "NAN":
loc = self.cursor
if not self.isint(loc):
return 1
loc = int(loc)
return self.source[loc]
def getpos(self):
return self.cursor
def getlen(self):
return len(self.source)
def delline(self, loc="NAN"):
if loc == "NAN":
loc = self.cursor
if not self.isint(loc):
return 1
loc = int(loc)
del self.source[loc]
And the corresponding entry in main.py
from editor import editor
import argparse
# Create the parserr
parser= argparse.ArgumentParser(description='JEDI is a Ed clone, made in the 21st Century')
# Add the arguments
parser.add_argument('file', type=str, help='The path used to access the file to edit (Ex: ~/.bashrc')
parser.add_argument('-p', nargs='?', const='', action='store', type=str, help='The prompt string to be used')
def split(word):
return [char for char in word]
args = parser.parse_args()
e = editor(args.file)
p = args.p
if p == 'None':
p=''
while True:
command = split(input(p))
if command[0] == 'a':
data = []
txt = ""
while txt != "`":
data.append(txt)
txt = input()
data.remove(data[0])
e.append(data)
elif command[0] == 'w':
e.write()
elif e.isint(command[0]):
e.goto(command[0])
elif command[0] == 'p':
if len(command) == 1:
print( e.getln())
elif len(split(command)) == 2:
print(e.getln(int(command[1])))
elif command[0] == 'd':
if len(command) == 1:
e.delline()
elif len(command) == 2:
error = e.delline(command[1])
elif command[0] == 'q':
break
NOTE: I have left a getpos() in editor.py for you to use to impliment the l command.
This command shoud print this:
{LINENO} \t {LINE}