How to print only uppercase letters in Python using isupper( ) method?

Question

I am trying to write a function that uses a for loop and the isupper method to print only the uppercase letters of a string.

what i have done so far:

upper_chars = ""
def only_upper(s):
    for char in s:
        if s.isupper() == True:
        upper_chars += char
 print upper_chars

But this is not working? Anyone tell me why? I get this error message: "UnboundLocalError: local variable 'upper_chars' referenced before assignment"

Answer 1

Several problems in your code:

• you should define upper_chars variable inside the function
• in the loop you should call isupper() on a character, not the whole string
• your function should return something
• you should call the function
• wrong indentation in the if block

Here's the code with fixes:

def only_upper(s):
    upper_chars = ""
    for char in s:
        if char.isupper():
            upper_chars += char
    return upper_chars

print only_upper("HeLLo WorLD")

---

Also, you can use filter():

def only_upper(s):
    return filter(lambda x: x.isupper(), s)

print only_upper("HeLLo WorLD")

Or:

def only_upper(s):
    return "".join(c for c in s if c.isupper())

print only_upper("HeLLo WorLD")

Both print:

HLLWLD