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def valid_paren(input_str):
# Declaraing a stack.
stack = []
# Iterating over the entire string
for paren in input_str:
# If the input string contains an opening parenthesis,
# push in on to the stack.
if paren == '(' or paren == '[' or paren == '{':
stack.append(paren)
else:
# In the case of valid parentheses, the stack cannot be
# be empty if a closing parenthesis is encountered.
if not stack:
print(input_str, "contains invalid parentheses.")
return
else:
# If the input string contains a closing bracket,
# then pop the corresponding opening parenthesis if
# present.
top = stack[-1]
if paren == ')' and top == '(' or \
paren == ']' and top == '[' or \
paren == '}' and top == '{':
stack.pop()
# Checking the status of the stack to determine the
# validity of the string.
if not stack:
print(input_str, "contains valid parentheses.")
else:
print(input_str, "contains invalid parentheses.")
input1 = "{{}}()[()]"
input2 = "{][}"
input3 = ")"
valid_paren(input1)
valid_paren(input2)
valid_paren(input3)
input4 = "([)]"
valid_paren(input4)
input5 = '() [{}]'
valid_paren(input5)
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