How to avoid writing request.GET.get() twice in order to print it?
Question:
I come from a PHP background and would like to know if there’s a way to do this in Python.
In PHP you can kill 2 birds with one stone like this:
Instead of:
if(getData()){
$data = getData();
echo $data;
}
I can do this:
if($data = getData()){
echo $data;
}
You check to see if getData() exists AND if it does, you assign it to a variable in one statement.
I wanted to know if there’s a way to do this in Python? So instead of doing this:
if request.GET.get('q'):
q = request.GET.get('q')
print q
avoid writing request.GET.get('q') twice.
Answers:
Probably not exactly what you were thinking, but…
q = request.GET.get('q')
if q:
print q
this?
See my 8-year-old recipe here for just this task.
# In Python, you can't code "if x=foo():" -- assignment is a statement, thus
# you can't fit it into an expression, as needed for conditions of if and
# while statements, &c. No problem, if you just structure your code around
# this. But sometimes you're transliterating C, or Perl, or ..., and you'd
# like your transliteration to be structurally close to the original.
#
# No problem, again! One tiny, simple utility class makes it easy...:
class DataHolder:
def __init__(self, value=None): self.value = value
def set(self, value): self.value = value; return value
def get(self): return self.value
# optional but handy, if you use this a lot, either or both of:
setattr(__builtins__,'DataHolder',DataHolder)
setattr(__builtins__,'data',DataHolder())
# and now, assign-and-set to your heart's content: rather than Pythonic
while 1:
line = file.readline()
if not line: break
process(line)
# or better in modern Python, but quite far from C-like idioms:
for line in file.xreadlines():
process(line)
# you CAN have your C-like code-structure intact in transliteration:
while data.set(file.readline()):
process(data.get())
Well, this would be one way
q = request.GET.get('q')
if q:
print q
A briefer (but not superior, due to the call to print of nothing) way would be
print request.GET.get('q') or '',
q = request.GET.get('q')
if q:
print q
else:
# q is None
...
There’s no way of doing assignment and conditionals in one go…
If get() throws an exception when it’s not there, you could do
try:
q = request.GET.get('q')
print q
except :
pass
A variation on Alex’s answer:
class DataHolder:
def __init__(self, value=None, attr_name='value'):
self._attr_name = attr_name
self.set(value)
def __call__(self, value):
return self.set(value)
def set(self, value):
setattr(self, self._attr_name, value)
return value
def get(self):
return getattr(self, self._attr_name)
save_data = DataHolder()
Usage:
if save_data(get_input()):
print save_data.value
or if you prefer an alternative interface:
if save_data.set(get_input()):
print save_data.get()
I would find this helpful to test a series of regular expressions in an if-elif-elif-elif etc construct, as in this SO question:
import re
input = u'test bar 123'
save_match = DataHolder(attr_name='match')
if save_match(re.search('foo (d+)', input)):
print "Foo"
print save_match.match.group(1)
elif save_match(re.search('bar (d+)', input)):
print "Bar"
print save_match.match.group(1)
elif save_match(re.search('baz (d+)', input)):
print "Baz"
print save_match.match.group(1)
config_hash = {}
tmp_dir = ([config_hash[x] for x in ["tmp_dir"] if config_hash.has_key(x)] or ["tmp"])[0]
print tmp_dir
config_hash["tmp_dir"] = "cat"
tmp_dir = ([config_hash[x] for x in ["tmp_dir"] if config_hash.has_key(x)] or ["tmp"])[0]
print tmp_dir
a possible way to do it, without necessity to set the variable before, could be like:
if (lambda x: globals().update({'q':x}) or True if x else False)(request.GET.get('q')):
print q
.. it’s just for fun – this method should not be used, because it is ugly hack, difficult to understand at first sight, and it creates/overwrites a global variable (only if the condition is met, though)
Simply try:
print(request.GET.get('q', ''))
which basically prints nothing if the first argument is not present (see dict.get).
Alternative solution would be to use a conditional expression in Python:
<expression1> if <condition> else <expression2>
but you’ll end up repeating variable twice, for example:
print(request.GET.get('q') if request.GET.get('q') else '')
For variable assignments in loops, check in here.
PEP 572 introduces Assignment Expressions. From Python 3.8 and onwards you can write:
if q := request.GET.get('q'):
print q
Here are some more examples from the Syntax and semantics part of the PEP:
# Handle a matched regex
if (match := pattern.search(data)) is not None:
# Do something with match
# A loop that can't be trivially rewritten using 2-arg iter()
while chunk := file.read(8192):
process(chunk)
# Reuse a value that's expensive to compute
[y := f(x), y**2, y**3]
# Share a subexpression between a comprehension filter clause and its output
filtered_data = [y for x in data if (y := f(x)) is not None]
I come from a PHP background and would like to know if there’s a way to do this in Python.
In PHP you can kill 2 birds with one stone like this:
Instead of:
if(getData()){
$data = getData();
echo $data;
}
I can do this:
if($data = getData()){
echo $data;
}
You check to see if getData() exists AND if it does, you assign it to a variable in one statement.
I wanted to know if there’s a way to do this in Python? So instead of doing this:
if request.GET.get('q'):
q = request.GET.get('q')
print q
avoid writing request.GET.get('q') twice.
Probably not exactly what you were thinking, but…
q = request.GET.get('q')
if q:
print q
this?
See my 8-year-old recipe here for just this task.
# In Python, you can't code "if x=foo():" -- assignment is a statement, thus
# you can't fit it into an expression, as needed for conditions of if and
# while statements, &c. No problem, if you just structure your code around
# this. But sometimes you're transliterating C, or Perl, or ..., and you'd
# like your transliteration to be structurally close to the original.
#
# No problem, again! One tiny, simple utility class makes it easy...:
class DataHolder:
def __init__(self, value=None): self.value = value
def set(self, value): self.value = value; return value
def get(self): return self.value
# optional but handy, if you use this a lot, either or both of:
setattr(__builtins__,'DataHolder',DataHolder)
setattr(__builtins__,'data',DataHolder())
# and now, assign-and-set to your heart's content: rather than Pythonic
while 1:
line = file.readline()
if not line: break
process(line)
# or better in modern Python, but quite far from C-like idioms:
for line in file.xreadlines():
process(line)
# you CAN have your C-like code-structure intact in transliteration:
while data.set(file.readline()):
process(data.get())
Well, this would be one way
q = request.GET.get('q')
if q:
print q
A briefer (but not superior, due to the call to print of nothing) way would be
print request.GET.get('q') or '',
q = request.GET.get('q')
if q:
print q
else:
# q is None
...
There’s no way of doing assignment and conditionals in one go…
If get() throws an exception when it’s not there, you could do
try:
q = request.GET.get('q')
print q
except :
pass
A variation on Alex’s answer:
class DataHolder:
def __init__(self, value=None, attr_name='value'):
self._attr_name = attr_name
self.set(value)
def __call__(self, value):
return self.set(value)
def set(self, value):
setattr(self, self._attr_name, value)
return value
def get(self):
return getattr(self, self._attr_name)
save_data = DataHolder()
Usage:
if save_data(get_input()):
print save_data.value
or if you prefer an alternative interface:
if save_data.set(get_input()):
print save_data.get()
I would find this helpful to test a series of regular expressions in an if-elif-elif-elif etc construct, as in this SO question:
import re
input = u'test bar 123'
save_match = DataHolder(attr_name='match')
if save_match(re.search('foo (d+)', input)):
print "Foo"
print save_match.match.group(1)
elif save_match(re.search('bar (d+)', input)):
print "Bar"
print save_match.match.group(1)
elif save_match(re.search('baz (d+)', input)):
print "Baz"
print save_match.match.group(1)
config_hash = {}
tmp_dir = ([config_hash[x] for x in ["tmp_dir"] if config_hash.has_key(x)] or ["tmp"])[0]
print tmp_dir
config_hash["tmp_dir"] = "cat"
tmp_dir = ([config_hash[x] for x in ["tmp_dir"] if config_hash.has_key(x)] or ["tmp"])[0]
print tmp_dir
a possible way to do it, without necessity to set the variable before, could be like:
if (lambda x: globals().update({'q':x}) or True if x else False)(request.GET.get('q')):
print q
.. it’s just for fun – this method should not be used, because it is ugly hack, difficult to understand at first sight, and it creates/overwrites a global variable (only if the condition is met, though)
Simply try:
print(request.GET.get('q', ''))
which basically prints nothing if the first argument is not present (see dict.get).
Alternative solution would be to use a conditional expression in Python:
<expression1> if <condition> else <expression2>
but you’ll end up repeating variable twice, for example:
print(request.GET.get('q') if request.GET.get('q') else '')
For variable assignments in loops, check in here.
PEP 572 introduces Assignment Expressions. From Python 3.8 and onwards you can write:
if q := request.GET.get('q'):
print q
Here are some more examples from the Syntax and semantics part of the PEP:
# Handle a matched regex
if (match := pattern.search(data)) is not None:
# Do something with match
# A loop that can't be trivially rewritten using 2-arg iter()
while chunk := file.read(8192):
process(chunk)
# Reuse a value that's expensive to compute
[y := f(x), y**2, y**3]
# Share a subexpression between a comprehension filter clause and its output
filtered_data = [y for x in data if (y := f(x)) is not None]