How to convert a dictionary to query string in Python?

Question

After using cgi.parse_qs(), how to convert the result (dictionary) back to query string? Looking for something similar to urllib.urlencode().

Kilocycle

N.B: cgi.parse_qs() is deprecated. Use urlparse.parse_qs() instead. – Therapsid

See also: #5608051 – Tungusic

Answer 1

Python 3

urllib.parse.urlencode(query, doseq=False, [...])

Convert a mapping object or a sequence of two-element tuples, which may contain str or bytes objects, to a percent-encoded ASCII text string.

— Python 3 urllib.parse docs

A dict is a mapping.

Legacy Python

urllib.urlencode(query[, doseq])
Convert a mapping object or a sequence of two-element tuples to a “percent-encoded” string... a series of key=value pairs separated by '&' characters...

— Python 2.7 urllib docs

Comment

This is true, but the dict returned by cgi.parse_qs() actually has lists as its "values". Passing these straight in will result in very odd looking query strings. – Therapsid

True enough. That'll teach me to read more than the first sentence! – Therapsid

urllib.parse.urlencode in Python 3. – Prowler

The problem is that urlencode will convert space into +, which is not recommended. – Planetary

@user1633272: Not recommended according to who? – Comment

is there a way that I can use urlencode() just to make use of doseq param. i.e. I do not want any of the characters to be encoded. I know there is a safe param, but that would require me to list out each character. I am looking for a wild-card character for safe param so that it understands that it has to encode nothing. – Canica

Based on my findings, I do not think anything like such^ exists. And thus, I am exploring the option to first let it get encode and then decode. I know its a round-trip, but I couldn't think of any other alternative except writing the logic of doseq on my own in my codebase. – Canica

I realised I can achieve this^^ by passing my own quote_via function. Something like: urlencode(params, doseq=True, quote_via=lambda a, b, c, d : a) – Canica

Instead of unquote_plus(urlencode(params, doseq=True)) – Canica

Answer 2

In python3, slightly different:

from urllib.parse import urlencode
urlencode({'pram1': 'foo', 'param2': 'bar'})

output: 'pram1=foo&param2=bar'

for python2 and python3 compatibility, try this:

try:
    #python2
    from urllib import urlencode
except ImportError:
    #python3
    from urllib.parse import urlencode

Subarid

Answer 3

You're looking for something exactly like urllib.urlencode()!

However, when you call parse_qs() (distinct from parse_qsl()), the dictionary keys are the unique query variable names and the values are lists of values for each name.

In order to pass this information into urllib.urlencode(), you must "flatten" these lists. Here is how you can do it with a list comprehenshion of tuples:

query_pairs = [(k,v) for k,vlist in d.iteritems() for v in vlist]
urllib.urlencode(query_pairs)

Therapsid

Or you could pass doseq=True. – Comment

@downvoter: How could I improve this answer? It has been six years since I wrote it! – Therapsid

Answer 4

Maybe you're looking for something like this:

def dictToQuery(d):
  query = ''
  for key in d.keys():
    query += str(key) + '=' + str(d[key]) + "&"
  return query

It takes a dictionary and convert it to a query string, just like urlencode. It'll append a final "&" to the query string, but return query[:-1] fixes that, if it's an issue.

Carbylamine

Have you met str.join() yet? How about urllib.quote_plus()? – Comment

@Carbylamine Your solution should work in simple cases. However, have a look urlencode in urllib.py (it should by in your Python install) to see why creating a query string is sometimes not quite as simple as your answer implies (in particular the need to 'quote' certain characters that aren't valid in a URL). @Ignacio has also referenced two functions that would clean up your implementation and make it correct. – Fishery

Ah, indeed. Sorry for the cruddy implementation. Goes to show I should be more careful answering questions I've never faced myself. – Carbylamine

While this may not be the best answer, it is exactly what I wanted to see when I clicked on this question's title. I have only 4 items in a dict that I need to turn into a name=value pair separated by an '&'. My values are controlled. The str.join() is handy in my case but I have no need for quote_plus(), again, because it's not public-facing code :) Thanks! – Notwithstanding

@Notwithstanding but the more correct way (from urllib.parse import urlencode; urlencode(your_dict)) is shorter and easier than this! I'll grant that it's sometimes smart to reinvent the wheel, even shoddily, when it's expensive or inconvenient to access existing, well-designed wheels, but here using the off-the-shelf wheel is easier and quicker than rolling your own inferior one. – Vat