pyfil 0.2

print the return value of python expression -- also in loops

This ain’t the first project of this kind, and it won’t be the last, but this one is special because it’s all mine. pyeval is a more mature project of a similar sort. Some might accuse pyeval of feature creep, but I would never do that, because I’m totally not jealous that they did it first. :D

Pretty sure there are other projects like this, too. It’s sort of an obvious thing to try to do.

pyfil gives you the rep command. This is because when I initially posted it in #python IRC channel, user [Tritium] (that ray of sunshine) said I had recreated the REP of the python REPL (read evaluate print loop). That is more or less the case. rep reads python expressions at the command line, evaluates them and prints them to stdout. It might be interesting as a quick calculator or to test something, like the Python REPL, but it also has some special flags for iterating on stdin and parsing JSON, which make it useful as a filter for shell one-liners or scripts (like Perl).

pyfil is in pypi (i.e. you can get it easily with pip, if you want)

usage

available objects

Automatically imports (unless overridden in ~/.config/pyfil-env.py):

sys, os, re, math, pprint from pprint, timeit from timeit and strftime from time.

If you’d like to specify a custom execution environment for rep, create ~/.config/pyfil-env.py and put things in it.

The execution environment also has a special object for stdin, creatively named stdin. This differs from sys.stdin in that it rstrips (aka chomps) all the lines when you iterate over it, and it has a property, stdin.l, which returns a list of the (rstripped) lines. pyfil is quite bullish about using rstrip because python’s print function will supply an additional newline, and if you just want the value of the text in the line, you almost never want the newline character. If you do want the newlines, access sys.stdin directly.

stdin inherits the rest of its methods from sys.stdin, so you can use stdin.read() to get a string of all lines, if that’s what you need.

looping over stdin

one can do simple loops with a generator expression. (note that any expression that evaluates to an iterator will print each item on a new line)

$ ls / | rep '(i.upper() for i in stdin)'
BIN@
BOOT/
DEV/
ETC/
HOME/
...

However, the -l/--loop flag rep loops over stdin in a context like this:

for i in map(str.rstrip, sys.stdin):
    expressions

Therefore, the above loop can also be written thusly:

$ ls / | rep -l 'i.upper()'

--pre and --post (-b and -e) options can be used to specify actions to run after the loop. Note that the –pre option is run with exec instead of eval, and therefore output is never printed, and statements may be used. This is for things like initializing container types. –post is automatically printed and statements are not allowed (unless –quiet is used). –loop is implied if either of these options are used.

Using -s/--split or -F/--field-sep for doing awk things also implies –loop. The resulting list is named f in the execution environment, in quazi-Perl fashion.

Suppressing output and using statements

by default, pyfil prints the return value of expressions. Because this uses eval() internally to get value, statements may not be used. exec() supports statements, but it does not return the value of expressions when they are evaluated. When the -q/–quiet flag is used, automatic printing is suppressed, and expressions are evaluated with exec, so statements, such as assignments, may be used. Values may still be printed explicitely.

json

by popular demand, pyfil can parse json objects from stdin with the -j/–json flag. They are passed into the environment as the j object. combining with the -l flag will treat stdin as one json object per line.