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How to replace all "&int-int" with the respective string slices in an input string?

I have a school project question (for Python) that goes like this:
Given a string_input such as "abcd&1-4efg", the function must remove the "&1-4" and insert the string slice from 1 to 4 where the "&1-4" was.
eg. if string_input = "abcd&1-4efg",
"&1-4" is removed.
The remaining characters are indexed as follows: a=0, b=1, c=2, d=3, e=4, f=5, g=6
The new string becomes:
"abcdbcdeefg"
I've managed to write a long chunk of code to do this, but I'm wondering if anyone has any more efficient solutions?
Things to note:
The instructions can include double digits (eg. &10-15)
If the index isn't found, the returned string should print "?" for every missing index
(eg. "abcd&5-10efgh" would return "abcdfgh???efgh")
Intructions can be back-to-back (eg. "&10-15abcdef&1-5&4-5pqrs")
The code I've written is:
def expand(text):
text += "|"
import string
digits_dash = string.digits + "-"
idx_ref_str = ""
replace_list = []
record_val = False
output_to_list = []
instruct = ""
and_idx_mark = 0
#builds replace_list & idx_ref_list
for idx in range(len(text)):
if text[idx] == "&" and record_val==True:
output_to_list.append(instruct)
output_to_list.append(and_idx_mark)
replace_list.append(output_to_list)
output_to_list, instruct, inst_idx, and_idx_mark = [],"",0,0
and_idx_mark = idx
continue
elif text[idx] == "&":
record_val = True
and_idx_mark = idx
continue
#executes if currently in instruction part
if record_val == True:
#adds to instruct
if text[idx] in digits_dash:
instruct += text[idx]
#take info, add to replace list
else:
output_to_list.append(instruct)
output_to_list.append(and_idx_mark)
replace_list.append(output_to_list)
output_to_list, instruct, inst_idx, and_idx_mark, record_val = [],"",0,0,False
#executes otherwise
if record_val == False:
idx_ref_str += text[idx]
idx_ref_str = idx_ref_str[:-1]
text = text[:-1]
#converts str to int indexes in replace list[x][2]
for item in replace_list:
start_idx = ""
end_idx = ""
#find start idx
for char in item[0]:
if char in string.digits:
start_idx += char
elif char == "-":
start_idx = int(start_idx)
break
#find end idx
for char in item[0][::-1]:
if char in string.digits:
end_idx = char + end_idx
elif char == "-":
end_idx = int(end_idx)
break
start_end_list = [start_idx,end_idx]
item+=start_end_list
#split text into parts in list
count = 0
text_block = ""
text_block_list = []
idx_replace = 0
for char in text:
if char == "&":
text_block_list.append(text_block)
text_block = ""
count += len(replace_list[idx_replace][0])
idx_replace +=1
elif count > 0:
count -= 1
else:
text_block += char
text_block_list.append(text_block)
#creates output str
output_str = ""
for idx in range(len(text_block_list)-1):
output_str += text_block_list[idx]
#creates to_add var to add to output_str
start_repl = replace_list[idx][1]
end_repl = replace_list[idx][1] + len(replace_list[idx][0])
find_start = replace_list[idx][2]
find_end = replace_list[idx][3]
if end_idx >= len(idx_ref_str):
gap = end_idx + 1 - len(idx_ref_str)
to_add = idx_ref_str[find_start:] + "?" * gap
else:
to_add = idx_ref_str[find_start:find_end+1]
output_str += to_add
output_str += text_block_list[-1]
return output_str

Here's how I would do it. Always open to criticism.
import re
s = 'abcd&1-4efg'
c = re.compile('&[0-9]+-[0-9]+')
if (m := c.search(s)):
a, b = m.span()
left = s[:a]
right = s[b:]
o = [int(x) for x in m.group(0)[1:].split('-')]
mid = (left+right)[o[0]:o[1]+1]
print(left + mid + right)

Best approach for converting lowerCamelCase to snake_case

I came across below mentioned scenario:
Input:-
parselTongue
Expected Output:-
parsel_tongue
My code:-
empty_string = ""
word = input()
if word.islower() == 1:
empty_string = empty_string + word
print(empty_string)
else:
for char in word:
char = str(char)
if char.isupper() == 1:
x = char
y = word.find(x)
print(char.replace(char, word[0:y] + "_" + char.lower() + word[y:]))
My output:-
parsel_tTongue
Please advice where i am going wrong as my output is coming as "parsel_tTongue" and not "parsel_tongue"

The more elegant solution would be just to implement the logic using comprehension.
word = input()
output= ''.join(c if not c.isupper() else f'_{c.lower()}' for c in word)
#output: 'parsel_tongue'

I believe that this approach could be better.
It prevents from situations where word contains not only letters but also special characters or numbers.
word = "camelCaseWord"
res = "" # sanke case word
# handle 1st upper character
if word[0].isupper():
word = word[0].lower() + word[1:]
for w in word:
# Only letter can be upper
if w.isupper():
res += "_" + w.lower()
else:
res += w
print(res)
>>> camel_case_word
if word = "camelCase3Wor& - > >>> camel_case3_wor&

no need for loop use regex
import re
name = 'parselTongue'
name = re.sub(r'(?<!^)(?=[A-Z])', '_', name).lower()
print(name) # camel_case_name

Adjust the slice on word
empty_string = ""
word = input()
if word.islower() == 1:
empty_string = empty_string + word
print(empty_string)
else:
for char in word:
char = str(char)
if char.isupper() == 1:
x = char
y = word.find(x)
print(char.replace(char, word[0:y] + "_" + char.lower()+ word[y+1:]))
prints the following for the input parselTongue
praselTongue
prasel_tongue

The best practice may be using regex:
fooBarBaz -> foo_bar_baz
re.sub(r'([A-Z])',lambda match:'_'+match.group(1).lower(),'fooBarBaz')
foo_bar_baz -> fooBarBaz
re.sub(r'_([a-z])',lambda match:match.group(1).upper(),'foo_bar_baz')

import re
camel_case = 'miaBau'
snake_case = re.sub(r'([A-Z])', r'_\1', camel_case).lower()

Replace a sequence of characters by another one

I have a sequence of characters '-------' and i want to replace each '-' in it by each letter in 'jaillir' in the correct range.
How do i do that ?
Here is my code
import random
with open ("lexique.txt", "r", encoding= "utf8") as a:
words = []
letters = []
tirets= []
for line in a:
ligne = line[:-1]
words.append(ligne)
choix = random.choice(words)
tiret = ('-'* len(choix))
print(tiret)
print(choix)
accompli = False
while not accompli:
lettre = input("Entrez une lettre du mot ")
for t in range(len(tiret)):
if lettre in choix:
tiret.replace(tiret[t], lettre[t])
print(tiret)

I think you need to fix your file reading code, even though it is not the question, as below:
with open('lexique.txt', r) as f:
text = f.read() # get file contents
Next to replace the ---- by a word, I am assuming that the dashes in your text will only ever be the same length as the word, so:
word = 'word' # any string e.g. word
dashes = '-' * len(word)
So now you can use python's string.replace method like so:
text = text.replace(dashes, word) # every time it finds the sequence of dashes it will be replaced by your word
With a for loop (gradual replacement):
word = 'word' # any word
length = len(word)
temp = ''
for i, letter in enumerate(text):
if letter == '-':
if i + len(tempword) < len(text):
characters = [True if l == '-' else False for l in text[i:i + len(tempword)]]
if not(False in characters):
new += tempword[0]
if len(tempword) > 1:
tempword = tempword[1:]
else:
tempword = word
else:
new += letter
else:
new += letter
print(new)

Replace all spaces in a string with underscores

How would I replace the spaces in a string with underscores without using the replace function. I was told to also use a accumulation string with some type of loop
string = input("Enter a string")
i = 0
acc = ""
for char in string:
if char == " ":
acc = string + "_"
print(acc)

Try this,
string = input("Enter a string")
i = 0
acc = ""
newlist = [] #create a new list which will be the output
strlist = list(string) #create a list of each character in the input string
for char in strlist:
if char == " ":
newlist.append('_')
newlist.append(char)
acc = ''.join(newlist)
print(acc)

Your code should to be :
string = input("Enter a string")
i = 0
acc = ""
for char in string:
if char == " ":
acc += "_"
else:
acc += char
print(acc)
Try it if without replace.
string = input("Enter a string")
res = ''.join(["_" if i == " " else i for i in string])
print(res)
Another method:
string = input("Enter a string")
res = "_".join(string.split(" "))
print(res)

Your code isn't too far off. You can use an accumulation string like this:
string = input("Enter a string")
acc = ""
for char in string:
if char == " ":
char = "_"
acc += char
print(acc)

If you are allowed to use split, then
s = 'Your string with spaces'
s_ = ''
for word in s.split():
s_ += '_' + word
s_[1:] # 'Your_string_with_spaces'
Otherwise, instead of words, concatenate characters with '_' instead of ' ':
s_ = ''
for char in s:
if char == ' ':
s_ += '_'
else:
s_ += char

How can I make this code shorter (less lines etc)

I am writing a code and want to make it as short as possible, is there any way i can?
text = raw_input("Give me some text > ")
list1 = []
for char in text:
num = ord(char)
if num in range(48,57):
print "ERROR 319: Number entered"
quit()
elif num in range(65,90) or num in range (97,122):
upper = char.upper()
list1.append(upper)
num1 = 0
vowelCount = 0
conCount = 0
for x in range(len(list1)):
if list1[num1] == "A" or list1[num1] == "E" or list1[num1] == "I" or list1[num1] == "O" or list1[num1] == "U":
vowelCount = vowelCount + 1
else:
conCount = conCount + 1
num1 = num1 + 1
print "Vowels: " +str(vowelCount) + " Consonants: " + str(conCount)

Instead of taking ord() of the character, you can use the string methods:
char.isdigit() # check if a char is a digit
char.isalpha() # check if char is letter
For checking the vowel counts, try:
vowel_count = len(filter(lambda c: c in "aeiou", list1))
cons_count = len(list1) - vowel_count

Building off of AmourK's answer, you could do something like this:
text = raw_input("Give me some text > ")
vowel_count = len(filter(lambda c: c in "aeiou", text))
cons_count = len(filter(lambda c: c not in "aeiou" and c.isalpha(), text))
print "Vowels: %d Consonants: %d" % (vowel_count, cons_count)