I'm trying to find way to parse string that can contain variable, function, list, or dict written in python syntax separated with ",". Whitespace should be usable anywhere, so split with "," when its not inside (), [] or {}.
Example string: "variable, function1(1,3), function2([1,3],2), ['list_item_1','list_item_2'],{'dict_key_1': "dict_item_1"}"
Another example string: "variable,function1(1, 3) , function2( [1,3],2), ['list_item_1','list_item_2'],{'dict_key_1': "dict_item_1"}"
Example output ["variable", "function1(1,3)", "function2([1,3],2)", "['list_item_1','list_item_2']", "{'dict_key_1': "dict_item_1"}"]
edit:
Reason for the code is to parse string an then run it with exec("var = &s" % list[x]). (yes i know this might not be recommended way to do stuff)
I guess the main problem here is that the arrays and dicts also have commas in them, so just using str.split(",") wouldn't work. One way of doing it is to parse the string one character at a time, and keep track of whether all brackets are closed. If they are, we can append the current result to an array when we come across a comma. Here's my attempt:
s = "variable, function1(1,3),function2([1,3],2),['list_item_1','list_item_2'],{'dict_key_1': 'dict_item_1'}"
tokens = []
current = ""
open_brackets = 0
for char in s:
current += char
if char in "({[":
open_brackets += 1
elif char in ")}]":
open_brackets -= 1
elif (char == ",") and (open_brackets == 0):
tokens.append(current[:-1].strip())
current = ""
tokens.append(current)
for t in tokens:
print(t)
"""
variable
function1(1,3)
function2([1,3],2)
['list_item_1','list_item_2']
{'dict_key_1': 'dict_item_1'}
"""
Regular expressions aren't very good for parsing the complexity of arbitrary code. What exactly are you trying to accomplish? You can (unsafely) use eval to just evaluate the string as code. Or if you're trying to understand it without evaling it, you can use the ast or dis modules for various forms of inspection.
Have you tried using split?
>>> teststring = "variable, function1(1,3), function2([1,3],2), ['list_item_1','list_item_2'],{'dict_key_1': 'dict_item_1'}"
>>> teststring.split(", ")
['variable', 'function1(1,3)', 'function2([1,3],2)', "['list_item_1','list_item_2'],{'dict_key_1': 'dict_item_1'}"]
Related
I just want to know if this is a good way or not.
Input_str = "random Str"
Output_str = ""
for i in range(len(Input_str)+1):
if i == 0: continue
Output_str += Input_str[-i]
print(Output_str)
To quickly reverse a string use the following code:
string = "string"
string[::-1]
>>> gnirts
It takes the entire string and iterates reversely over it .
There is a better and more pythonistic way to do this (although your code works just fine).
output_str = input_str[::-1]
This will pretty much do exactly what your code does - it will iterate from the end of the string towards the front and save that reversed string into the new variable.
You can read more about this syntax called string slicing here.
I'm learning Python and have been taking an online class. This class was very basic and I am know trying to continue my studies elsewhere. Stackoverflow.com has helped me a great deal. In the online course we didn't cover a lot about return statements, which I am now trying to learn. I would like to do something very basic, so I was thinking of creating a program that would receive a string as an argument without having any return value. I want the user to type a word that will be shown with characters or symbols between every letter.
Example
User types in the word Python.
The word will be shown as =P=y=t=h=o=n= or -P-y-t-h-o-n- or maybe with * between every letter.
Is this an easy task? Can someone help me how to go about doing this?
Thank you.
Joel
If you want to do it yourself, you can go through your string like this:
my_string = "Python"
for letter in my_string:
# do something with the letter
print(letter)
This will print each letter in your word. What you want to do is having a new string with your desired character. You probably know you can concatenate (append) two strings in this way :
str1 = "hello"
str2 = "world"
str3 = str1 + str2
print(str3) #helloworld
So to do what you'd like to do, you can see each letter as a substring of your main string, and your desired character (for example *) as another string, and build a result string in that way.
inputString = "Python"
result = ""
myChar = "*"
for letter in inputString:
# build your result
build = build + letter
print(build)
This will just copy inputString into result, though I think you'll have understood how to use it in order to add your custom chars between the letters.
Yes python makes this sort of string manipulation very easy (some other languages... not so much). Look up the standard join function in the python docs.
def fancy_print(s, join_char='-'):
# split string into a list of characters
letters = list(s)
# create joined string
output = join_char + join_char.join(letters) + join_char
# show it
print(output)
then
>>> fancy_print("PYTHON")
-P-Y-T-H-O-N-
>>> fancy_print("PYTHON", "*")
*P*Y*T*H*O*N*
There is a string, for example. EXAMPLE.
How can I remove the middle character, i.e., M from it? I don't need the code. I want to know:
Do strings in Python end in any special character?
Which is a better way - shifting everything right to left starting from the middle character OR creation of a new string and not copying the middle character?
In Python, strings are immutable, so you have to create a new string. You have a few options of how to create the new string. If you want to remove the 'M' wherever it appears:
newstr = oldstr.replace("M", "")
If you want to remove the central character:
midlen = len(oldstr) // 2
newstr = oldstr[:midlen] + oldstr[midlen+1:]
You asked if strings end with a special character. No, you are thinking like a C programmer. In Python, strings are stored with their length, so any byte value, including \0, can appear in a string.
To replace a specific position:
s = s[:pos] + s[(pos+1):]
To replace a specific character:
s = s.replace('M','')
This is probably the best way:
original = "EXAMPLE"
removed = original.replace("M", "")
Don't worry about shifting characters and such. Most Python code takes place on a much higher level of abstraction.
Strings are immutable. But you can convert them to a list, which is mutable, and then convert the list back to a string after you've changed it.
s = "this is a string"
l = list(s) # convert to list
l[1] = "" # "delete" letter h (the item actually still exists but is empty)
l[1:2] = [] # really delete letter h (the item is actually removed from the list)
del(l[1]) # another way to delete it
p = l.index("a") # find position of the letter "a"
del(l[p]) # delete it
s = "".join(l) # convert back to string
You can also create a new string, as others have shown, by taking everything except the character you want from the existing string.
How can I remove the middle character, i.e., M from it?
You can't, because strings in Python are immutable.
Do strings in Python end in any special character?
No. They are similar to lists of characters; the length of the list defines the length of the string, and no character acts as a terminator.
Which is a better way - shifting everything right to left starting from the middle character OR creation of a new string and not copying the middle character?
You cannot modify the existing string, so you must create a new one containing everything except the middle character.
Use the translate() method:
>>> s = 'EXAMPLE'
>>> s.translate(None, 'M')
'EXAPLE'
def kill_char(string, n): # n = position of which character you want to remove
begin = string[:n] # from beginning to n (n not included)
end = string[n+1:] # n+1 through end of string
return begin + end
print kill_char("EXAMPLE", 3) # "M" removed
I have seen this somewhere here.
card = random.choice(cards)
cardsLeft = cards.replace(card, '', 1)
How to remove one character from a string:
Here is an example where there is a stack of cards represented as characters in a string.
One of them is drawn (import random module for the random.choice() function, that picks a random character in the string).
A new string, cardsLeft, is created to hold the remaining cards given by the string function replace() where the last parameter indicates that only one "card" is to be replaced by the empty string...
On Python 2, you can use UserString.MutableString to do it in a mutable way:
>>> import UserString
>>> s = UserString.MutableString("EXAMPLE")
>>> type(s)
<class 'UserString.MutableString'>
>>> del s[3] # Delete 'M'
>>> s = str(s) # Turn it into an immutable value
>>> s
'EXAPLE'
MutableString was removed in Python 3.
Another way is with a function,
Below is a way to remove all vowels from a string, just by calling the function
def disemvowel(s):
return s.translate(None, "aeiouAEIOU")
Here's what I did to slice out the "M":
s = 'EXAMPLE'
s1 = s[:s.index('M')] + s[s.index('M')+1:]
To delete a char or a sub-string once (only the first occurrence):
main_string = main_string.replace(sub_str, replace_with, 1)
NOTE: Here 1 can be replaced with any int for the number of occurrence you want to replace.
You can simply use list comprehension.
Assume that you have the string: my name is and you want to remove character m. use the following code:
"".join([x for x in "my name is" if x is not 'm'])
If you want to delete/ignore characters in a string, and, for instance, you have this string,
"[11:L:0]"
from a web API response or something like that, like a CSV file, let's say you are using requests
import requests
udid = 123456
url = 'http://webservices.yourserver.com/action/id-' + udid
s = requests.Session()
s.verify = False
resp = s.get(url, stream=True)
content = resp.content
loop and get rid of unwanted chars:
for line in resp.iter_lines():
line = line.replace("[", "")
line = line.replace("]", "")
line = line.replace('"', "")
Optional split, and you will be able to read values individually:
listofvalues = line.split(':')
Now accessing each value is easier:
print listofvalues[0]
print listofvalues[1]
print listofvalues[2]
This will print
11
L
0
Two new string removal methods are introduced in Python 3.9+
#str.removeprefix("prefix_to_be_removed")
#str.removesuffix("suffix_to_be_removed")
s='EXAMPLE'
In this case position of 'M' is 3
s = s[:3] + s[3:].removeprefix('M')
OR
s = s[:4].removesuffix('M') + s[4:]
#output'EXAPLE'
from random import randint
def shuffle_word(word):
newWord=""
for i in range(0,len(word)):
pos=randint(0,len(word)-1)
newWord += word[pos]
word = word[:pos]+word[pos+1:]
return newWord
word = "Sarajevo"
print(shuffle_word(word))
Strings are immutable in Python so both your options mean the same thing basically.
I have a list containing the lines of a file.
list1[0]="this is the first line"
list2[1]="this is the second line"
I also have a string.
example="TTTTTTTaaaaaaaaaabcccddeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeefffff"
I want to replace list[0] with the string (example). However I want to keep the word length. For example the new list1[0] should be "TTTT TT TTa aaaaa aaaa". The only solution I could come up with was to turn the string example into a list and use a for loop to read letter by letter from the string list into the original list.
for line in open(input, 'r'):
list1[i] = listString[i]
i=i+1
However this does not work from what I understand because Python strings are immutable? What's a good way for a beginner to approach this problem?
I'd probably do something like:
orig = "this is the first line"
repl = "TTTTTTTaaaaaaaaaabcccddeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeefffff"
def replace(orig, repl):
r = iter(repl)
result = ''.join([' ' if ch.isspace() else next(r) for ch in orig])
return result
If repl could be shorter than orig, consider r = itertools.cycle(repl)
This works by creating an iterator out of the replacement string, then iterating over the original string, keeping the spaces, but using the next character from the replacement string instead of any non-space characters.
The other approach you could take would be to note the indexes of the spaces in one pass through orig, then insert them at those indexes in a pass of repl and return a slice of the result
def replace(orig, repl):
spaces = [idx for idx,ch in enumerate(orig) if ch.isspace()]
repl = list(repl)
for idx in spaces:
repl.insert(idx, " ")
# add a space before that index
return ''.join(repl[:len(orig)])
However I couldn't imagine the second approach to be any faster, is certain to be less memory-efficient, and I don't find it easier to read (in fact I find it HARDER to read!) It also don't have a simple workaround if repl is shorter than orig (I guess you could do repl *= 2 but that's uglier than sin and still doesn't guarantee it'll work)
There is a string, for example. EXAMPLE.
How can I remove the middle character, i.e., M from it? I don't need the code. I want to know:
Do strings in Python end in any special character?
Which is a better way - shifting everything right to left starting from the middle character OR creation of a new string and not copying the middle character?
In Python, strings are immutable, so you have to create a new string. You have a few options of how to create the new string. If you want to remove the 'M' wherever it appears:
newstr = oldstr.replace("M", "")
If you want to remove the central character:
midlen = len(oldstr) // 2
newstr = oldstr[:midlen] + oldstr[midlen+1:]
You asked if strings end with a special character. No, you are thinking like a C programmer. In Python, strings are stored with their length, so any byte value, including \0, can appear in a string.
To replace a specific position:
s = s[:pos] + s[(pos+1):]
To replace a specific character:
s = s.replace('M','')
This is probably the best way:
original = "EXAMPLE"
removed = original.replace("M", "")
Don't worry about shifting characters and such. Most Python code takes place on a much higher level of abstraction.
Strings are immutable. But you can convert them to a list, which is mutable, and then convert the list back to a string after you've changed it.
s = "this is a string"
l = list(s) # convert to list
l[1] = "" # "delete" letter h (the item actually still exists but is empty)
l[1:2] = [] # really delete letter h (the item is actually removed from the list)
del(l[1]) # another way to delete it
p = l.index("a") # find position of the letter "a"
del(l[p]) # delete it
s = "".join(l) # convert back to string
You can also create a new string, as others have shown, by taking everything except the character you want from the existing string.
How can I remove the middle character, i.e., M from it?
You can't, because strings in Python are immutable.
Do strings in Python end in any special character?
No. They are similar to lists of characters; the length of the list defines the length of the string, and no character acts as a terminator.
Which is a better way - shifting everything right to left starting from the middle character OR creation of a new string and not copying the middle character?
You cannot modify the existing string, so you must create a new one containing everything except the middle character.
Use the translate() method:
>>> s = 'EXAMPLE'
>>> s.translate(None, 'M')
'EXAPLE'
def kill_char(string, n): # n = position of which character you want to remove
begin = string[:n] # from beginning to n (n not included)
end = string[n+1:] # n+1 through end of string
return begin + end
print kill_char("EXAMPLE", 3) # "M" removed
I have seen this somewhere here.
card = random.choice(cards)
cardsLeft = cards.replace(card, '', 1)
How to remove one character from a string:
Here is an example where there is a stack of cards represented as characters in a string.
One of them is drawn (import random module for the random.choice() function, that picks a random character in the string).
A new string, cardsLeft, is created to hold the remaining cards given by the string function replace() where the last parameter indicates that only one "card" is to be replaced by the empty string...
On Python 2, you can use UserString.MutableString to do it in a mutable way:
>>> import UserString
>>> s = UserString.MutableString("EXAMPLE")
>>> type(s)
<class 'UserString.MutableString'>
>>> del s[3] # Delete 'M'
>>> s = str(s) # Turn it into an immutable value
>>> s
'EXAPLE'
MutableString was removed in Python 3.
Another way is with a function,
Below is a way to remove all vowels from a string, just by calling the function
def disemvowel(s):
return s.translate(None, "aeiouAEIOU")
Here's what I did to slice out the "M":
s = 'EXAMPLE'
s1 = s[:s.index('M')] + s[s.index('M')+1:]
To delete a char or a sub-string once (only the first occurrence):
main_string = main_string.replace(sub_str, replace_with, 1)
NOTE: Here 1 can be replaced with any int for the number of occurrence you want to replace.
You can simply use list comprehension.
Assume that you have the string: my name is and you want to remove character m. use the following code:
"".join([x for x in "my name is" if x is not 'm'])
If you want to delete/ignore characters in a string, and, for instance, you have this string,
"[11:L:0]"
from a web API response or something like that, like a CSV file, let's say you are using requests
import requests
udid = 123456
url = 'http://webservices.yourserver.com/action/id-' + udid
s = requests.Session()
s.verify = False
resp = s.get(url, stream=True)
content = resp.content
loop and get rid of unwanted chars:
for line in resp.iter_lines():
line = line.replace("[", "")
line = line.replace("]", "")
line = line.replace('"', "")
Optional split, and you will be able to read values individually:
listofvalues = line.split(':')
Now accessing each value is easier:
print listofvalues[0]
print listofvalues[1]
print listofvalues[2]
This will print
11
L
0
Two new string removal methods are introduced in Python 3.9+
#str.removeprefix("prefix_to_be_removed")
#str.removesuffix("suffix_to_be_removed")
s='EXAMPLE'
In this case position of 'M' is 3
s = s[:3] + s[3:].removeprefix('M')
OR
s = s[:4].removesuffix('M') + s[4:]
#output'EXAPLE'
from random import randint
def shuffle_word(word):
newWord=""
for i in range(0,len(word)):
pos=randint(0,len(word)-1)
newWord += word[pos]
word = word[:pos]+word[pos+1:]
return newWord
word = "Sarajevo"
print(shuffle_word(word))
Strings are immutable in Python so both your options mean the same thing basically.