擅长:python、mysql、java
<pre><code>def double_char(str): # function double_char takes argument str
double_char = "" # create an empty string assign to variable double_char. In python you put "" or '' around text that you want as a string (text).
for i in range(len(str)): # iterate from 0 to length of string
double_char += str[i]*2 # append character at position i from str and duplicate it
return double_char # return double_char
</code></pre>