Simple string manipulation

For Python, we could assign a string to a variable without defining it in the first place:

>>> x="This is great"
>>> type(x)
<class 'str'>

For the formula to convert an effective rate to another one, the second input value is a string. For example, 's2a':

>>> type='s2a'
>>> type[0]
's'
>>> len(type)
3

The len() function shows the length of a string, see the following code:

>>>x='Hello World!'
>>>len(x)
13

Here are several widely used ways to select substring:

string='Hello World!'

# find the length of the string
n_length=len(string)
print(n_length)

# the number of appearance of letter l
n=string.count('l') 
print(n) 

# find teh locatoin of work of 'World'
loc=string.index("World") 
print(loc) 

# number of spaces
n2=string.count(' ')
print(n2)

print(string[0]) # print the first letter 
print...