Why Doesn't Calling a String Method Do Anything Unless Its Output Is Assigned

Why doesn't calling a string method do anything unless its output is assigned?

This is because strings are immutable in Python.

Which means that X.replace("hello","goodbye") returns a copy of X with replacements made. Because of that you need replace this line:

X.replace("hello", "goodbye")

with this line:

X = X.replace("hello", "goodbye")

More broadly, this is true for all Python string methods that change a string's content "in-place", e.g. replace,strip,translate,lower/upper,join,...

You must assign their output to something if you want to use it and not throw it away, e.g.

X  = X.strip(' \t')
X2 = X.translate(...)
Y  = X.lower()
Z  = X.upper()
A  = X.join(':')
B  = X.capitalize()
C  = X.casefold()

and so on.

String method doesn`t work in Function // Python

You need to store the replace function return value in the same or diff variable.

testString = "Upper and Lower Case CALCULATION"

def case_counter(string, upperCount = 0, lowerCount = 0):
    string = string.replace(" ","") # Modified
    for i in string:
        if i.isupper():
            upperCount += 1
        else:
            lowerCount += 1

    print("Upper Letters count: ", upperCount)
    print("Lower Letters count: ", lowerCount)

case_counter(testString)
print("\n")

Also, I would like to suggest the best approach for this.

def case_counter(string):
   string = string.replace(" ","")
   upper_count = sum(i.isupper() for i in string)
   lower_count = len(string) - upper_count
   
   print("Upper Letters count: ", upper_count)
   print("Lower Letters count: ", lower_count)

Why is this list not replacing the string values?

The i.replace() returns the replaced string, but you have to assign it. So:

i = i.replace("hpp", "h")

Now i will contain the replaced string.

Why string method on a string object doesn't modify the object in Python?

Strings are immutable types in python. Main advantages of being immutable would be:

• simplify multithreaded programming.
• can be used as dictionary keys (will keep the same hash)

Error encountered while changing case of the letter

You are not saving the lowercased string to a new variable. Try:

name1 = "name1".lower()
print(name1)

Why doesn't Python return an error for string assignment using replace in a for loop?

a.replace(i, "B")

does not change the original string a. Instead, it returns the string which results from replacing i in a.
In your loop, you are merely evaluating an expression and dropping it on the floor.

You could do it this way:

a = "AECD"

for i in a:
    if i == "E":
        a = a.replace(i, "B")
        print(a)

In this version, you take the string with the replacement, and you assign that value to the variable a, which gives you the effect you were expecting.

Replacing character in string doesn't do anything

You can use re.sub. In particular, note that it can take a function as repl parameter. The function takes a match object, and returns the desired replacement based on the information the match object has (e.g., m.group(1)).

import re

lst = ['Therefore', 'allowance', '(#)', 't(o)o', 'perfectly', 'gentleman', '(##)', 'su(p)posing', 'man', 'his', 'now']

def remove_paren(m):
    return m.group(0) if m.group(1) in ('#', '##') else m.group(1)

output = [re.sub(r"\((.*?)\)", remove_paren, word) for word in lst]
print(output) # ['Therefore', 'allowance', '(#)', 'too', 'perfectly', 'gentleman', '(##)', 'supposing', 'man', 'his', 'now']

---

Related Topics