course-work/prep-work
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

rpn yo

Browse Source
This commit is contained in:
Armen Vartan 2014-12-02 15:14:47 -05:00
parent a8b7f2ddef
commit 40c5e73f28
1 changed files with 18 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
python/10-reverse-polish-notation/README.md
View File

@ -6,34 +6,36 @@ You've never done it until you've done it reverse polish.
I don't know what that means, but check this out on [reverse polish notation](http://en.wikipedia.org/wiki/Reverse_Polish_notation). I don't know what that means, but check this out on [reverse polish notation](http://en.wikipedia.org/wiki/Reverse_Polish_notation).
Reverse polish notation is a mathematical notation in which every operator follows all of its operands. For example: Reverse polish notation is a mathematical notation in which every operator follows all of its operands. For example:
```
3 4 + >>> 7 3 4 + = 7
4 2 / >>> 2 4 2 / = 2
10 7 2 - * 5 / >>> 10 10 7 2 - * 5 / = 10
```
Write a program that accepts a RPN equation as a command line argument, such that you would execute your program: Write a program that accepts a RPN equation as a command line argument, such that you would execute your program:
```
python3 rpn_calc.py 10 9 - 5 + python3 rpn_calc.py 10 9 - 5 +
```
Which would then return you 6, the result of that equation. Which would then return you 6, the result of that equation.
###ARGV #### ARGV
To run the program like this you need to import the sys library and access sys.argv. To run the program like this you need to import the sys library and access sys.argv.
ARGV gives us the arguments used to launch the program as an array. The first position is always the application name / file. The next are all others divided by spaces. ARGV gives us the arguments used to launch the program as an array. The first position is always the application name / file. The next are all others divided by spaces.
Read about sys.argv [here](http://www.pythonforbeginners.com/system/python-sys-argv) Read about sys.argv [here](http://www.pythonforbeginners.com/system/python-sys-argv)
Sandbox with this so you know what you are getting as an input. Sandbox with it, so you know what you are getting as an input.
Here's a nice hint - we can "slice" arrays in Python like in JS just by doing: Here's a nice hint - we can "slice" arrays in Python like in JS just by doing:
```
>>> array = ['hi', 'wut', 'm8', 'lol', 'doge']
>>> array[2:4]
['m8', 'lol']
```
array = ['hi', 'wut', 'm8', 'lol', 'doge'] #### Testing
array[2:4] ### returns ['m8', 'lol']
###Testing
Write some assert statements after you've solved the challenge. Write some assert statements after you've solved the challenge.
NOTE: You might need to escape the multiplication operator * when you pass it in. **NOTE**: You might need to escape the multiplication operator * when you pass it in. You can escape things by adding a backslash (\) in front of it.