How to read a string one letter at a time in python

Question

I need to convert a string inputed by a user into morse code  The way our professor wants us to do this is to read from a morseCode txt file  seperate the letters from the morseCode into two lists  then convert each letter to morse code  inserting a new line when there is a space    I have the beginning  What it does is reads the morseCode txt file and seperates the letters into a list  A  B      Z  and the codes into a list                       n                      n        We haven t learned  sets  yet  so I can t use that  How would I then take the string that they inputed  go through letter by letter  and convert it to morse code  I m a bit caught up  Here s what I have right now  not much at all      EDIT  completed the program     open morseCode txt file to read morseCodeFile   open  morseCode txt    r     format is  lt letter gt   lt morse code translation gt  lt  n gt       create an empty list for letters letterList            create an empty list for morse codes codeList        read the first line of the morseCode txt line   morseCodeFile readline         while the line is not empty while line                      strip the  n from the end of each line     line   line rstrip                 append the first character of the line to the letterList             letterList append line 0                    append the 3rd to last character of the line to the codeList     codeList append line 2                  read the next line     line   morseCodeFile readline             close the file     morseCodeFile close     try        get user input     print  Enter a string to convert to morse code or press  lt enter gt  to quit           userInput   input             while the user inputs something  continue        while userInput            strip the spaces from their input         userInput   userInput replace                    convert to uppercase         userInput   userInput upper              set string accumulator         accumulateLetters                go through each letter of the word         for x in userInput                            get the index of the letterList using x             index   letterList index x                get the morse code value from the codeList using the index found above             value   codeList index                accumulate the letter found above             accumulateLetters    value           print the letters             print accumulateLetters            input to try again or  lt enter gt  to quit         print  Try again or press  lt enter gt  to quit           userInput   input      except ValueError      print  Error in input  Only alphanumeric characters  a comma  and period allowed       main

User · Answer

A couple of things for ya   The loading would be  better  like this   with file  morsecodes txt    rt   as f     for line in f        line   line strip         if len line   gt  0             do your stuff to parse the file   That way you don t need to close  and you don t need to manually load each line  etc   etc   for letter in userInput     if ValidateLetter letter      you need to define this       code   GetMorseCode letter     from my other answer         do whatever you want

User · Answer

Use  index    def GetMorseCode letter      index   letterList index letter     code   codeList index     return code   Of course  you ll want to validate your input letter  convert its case as necessary  make sure it s in the list in the first place by checking that index    -1   but that should get you down the path

User · Answer

Retain a map of the Morse code conversion         Read map from file  add it to the datastructure morseCodeFile   file  morseCode txt   for line in moreCodeFile      conversion line 0     line 2   morseCodeFile close      Ask for input from the user s   raw input  Please enter string to translate     Go over each character  and print it the translation    Defensive programming  do something sane if the user    inputs non-Morse compatible strings      for c in s      print conversion get c   No translation for   c

User · Answer

I can t leave this question in this state with that final code in the question hanging over me     dan  here s a much neater and shorter version of your code  It would be a good idea to look at how this is done and code more this way in future  I realise you probably have no further need of this code  but learning how you should do it is a good idea  Some things to note    There are only two comments - and even the second is not really necessary for someone familiar with Python  they ll realise NL is being stripped  Only write comments where it adds value  The with statement  recommended in another answer  removes the bother of closing the file through the context handler  Use a dictionary instead of two lists  A generator comprehension   x for y in z   is used to do the translation in one line  Wrap as little code as you can in a try except block to reduce the probability of catching an exception you didn t mean to  Use the input   argument rather than print  ing first - Use   n  to get the new line you want  Don t write code across multiple lines or with intermediate variables like this just for the sake of it   a   a b   a   a c   b   a x   c   b y     Instead  write these constructs like this  chaining the calls as is perfectly valid   a   a b   c   c   a x   y        32   code      with open  morseCode txt    r   as morse code file        line format is  lt letter gt   lt morse code translation gt      for line in morse code file          line   line rstrip      Remove NL         code line 0     line 2    user input   input  Enter a string to convert to morse code or press  lt enter gt  to quit n   while user input      try          print    join code x  for x in user input replace          upper         except KeyError          print  Error in input  Only alphanumeric characters  a comma  and period allowed        user input   input  Try again or press  lt enter gt  to quit n

User · Answer

Create a lookup table first   morse    None     ord  z   - ord  a     1  for line in moreCodeFile      morse ord line 0  lower    - ord  a      line 2     Then convert using the table   for ch in userInput      print morse ord ch lower    - ord  a

User · Answer

For the actual processing I d keep a string of finished product  and loop through each letter in the string they have entered  I d call a function to convert a letter to morse code  then add it to the string of existing morse code   finishedProduct      userInput   input  Enter text   for letter in userInput      finishedProduct append  letterToMorseCode letter    theString      join finishedProduct  print theString    You could either check for space in the loop  or in the function that is called

User · Answer

Open the file f   open  morseCode txt    r      Read the morse code data into  letters    lowercased letter  morse code        letters      for Line in f      if not Line strip    break     letter  code   Line strip   split     Assuming the format is  lt letter gt  lt whitespace gt  lt morse code gt  lt newline gt      letters append  letter lower    code   f close      Get the input from the user    Don t use input   - it calls eval raw input      i   raw input  Enter a string to be converted to morse code or press  lt enter gt  to quit        Convert the codes to morse code out      for c in i      found   False     for letter  code in letters          if letter    c lower                found   True             out append code              break      if not found           raise Exception  invalid character   s    c     Print the output print     join out

User · Answer

Why not just iterate through the string   a string  abcd  for letter in a string      print letter   returns  a b c d   So  in pseudo-ish code  I would do this   user string   raw input   list of output      for letter in user string     list of output append morse code ify letter    output string      join list of output    Note  the morse code ify function is pseudo-code   You definitely want to make a list of the characters you want to output rather than just concatenating on them on the end of some string  As stated above  it s O n 2   bad  Just append them onto a list  and then use    join the list    As a side note  why are you removing the spaces  Why not just have morse code ify      return a   n

[python] How to read a string one letter at a time in python

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