Python Dictionary Sorting, filter, and lambda Function Tutorial

When automating payment tests, a signature must be generated, requiring a specific ordering of dictionary keys; this article explains how to sort a Python dict by removing entries with empty, zero, "0", dict or list values and then ordering the remaining keys alphabetically.

It provides a sample test_data dictionary containing various edge cases such as empty strings, numeric strings, nested JSON strings, URLs, and list values.

The required sorting steps are described, followed by an overview of essential Python built‑in functions and modules used in the process: dict, filter, lambda, sorted, eval, upper, and the hashlib.md5 module.

The article then details the dict constructor, showing several creation patterns with examples:

dict()
dict(a='a', b='b', t='t')
dict(zip(['one','two','three'], [1,2,3]))
dict([('one',1),('two',2),('three',3)])

Next, the filter function is introduced, explaining its signature, parameters, and return value, and a concrete example that extracts odd numbers from a list is given:

def is_odd(n):
    return n % 2 == 1
newlist = filter(is_odd, [1,2,3,4,5,6,7,8,9,10])
print(newlist)

A second filter example demonstrates selecting numbers whose square root is an integer within 1‑100:

import math

def is_sqr(x):
    return math.sqrt(x) % 1 == 0
newlist = filter(is_sqr, range(1,101))
print(newlist)

The article then covers lambda expressions, their syntax, and typical use‑cases, providing examples such as adding two numbers and sorting a list by absolute value:

add = lambda x, y: x + y
list1 = [3,5,-4,-1,0,-2,-6]
sorted(list1, key=lambda x: abs(x))

Finally, a closure example shows how a lambda can be returned from a function:

def get_y(a,b):
    return lambda x: a*x + b
y1 = get_y(1,1)
y1(1)  # returns 2

The article concludes with a reminder that while lambda can make code concise, explicit functions are often clearer, following the Python Zen principle “Explicit is better than implicit”.