when using a default value for a dictionary the comprehensive loop show empty list when asked to iterate for all key items
from collections import defaultdict
dict = {'whiz':1,'beerus':2,'vegeta':3,'goku':4}
dict = defaultdict(lambda : 'picalo')
print ([key for key in dict])
[]
process finished with exit code 0
this code is run in pycharm
Welcome to SO. Please include a description of expected behavior with your questions, or you'll get answers like this:
That's because there's nothing in the dictionary, it just has a default value!
As far as I can tell the error you're making is you're replacing your dictionary, not giving it a default value.
I think what you're looking for is something like this:
from collections import defaultdict
my_dict = {'whiz': 1,'beerus': 2,'vegeta': 3,'goku': 4}
my_dict = defaultdict(lambda: 'picalo', **my_dict)
print(my_dict)
Notice how I named the variable my_dict instead of dict, that's because dict is the "built-in" dictionary type and generally shouldn't be overwritten (to prevent bugs down the line).
Related
Maybe it is ordinary issue regarding iterating thru a dict. Please find below imovel.txt file, whose content is as follows:
{'Andar': ['primeiro', 'segundo', 'terceiro'], 'Apto': ['101','201','301']}
As you can see this is not a ordinary dictionary, with a key value pair; but a key with a list as key and another list as value
My code is:
#/usr/bin/python
def load_dict_from_file():
f = open('../txt/imovel.txt','r')
data=f.read()
f.close()
return eval(data)
thisdict = load_dict_from_file()
for key,value in thisdict.items():
print(value)
and yields :
['primeiro', 'segundo', 'terceiro'] ['101', '201', '301']
I would like to print a key,value pair like
{'primeiro':'101, 'segundo':'201', 'terceiro':'301'}
Given such txt file above, is it possible?
You should use the builtin json module to parse but either way, you'll still have the same structure.
There are a few things you can do.
If you know both of the base key names('Andar' and 'Apto') you can do it as a one line dict comprehension by zipping the values together.
# what you'll get from the file
thisdict = {'Andar': ['primeiro', 'segundo', 'terceiro'], 'Apto': ['101','201','301']}
# One line dict comprehension
newdict = {key: value for key, value in zip(thisdict['Andar'], thisdict['Apto'])}
print(newdict)
If you don't know the names of the keys, you could call next on an iterator assuming they're the first 2 lists in your structure.
# what you'll get from the file
thisdict = {'Andar': ['primeiro', 'segundo', 'terceiro'], 'Apto': ['101','201','301']}
# create an iterator of the values since the keys are meaningless here
iterator = iter(thisdict.values())
# the first group of values are the keys
keys = next(iterator, None)
# and the second are the values
values = next(iterator, None)
# zip them together and have dict do the work for you
newdict = dict(zip(keys, values))
print(newdict)
As other folks have noted, that looks like JSON, and it'd probably be easier to parse it read through it as such. But if that's not an option for some reason, you can look through your dictionary this way if all of your lists at each key are the same length:
for i, res in enumerate(dict[list(dict)[0]]):
ith_values = [elem[i] for elem in dict.values()]
print(ith_values)
If they're all different lengths, then you'll need to put some logic to check for that and print a blank or do some error handling for looking past the end of the list.
Lets say I have a key:value pair that I want to print, but it is itself inside a dictionary (it's actually JSON data):
cslfJson = {'displayFieldName': 'CSLF_ID', 'fieldValues': {'OBJECTID': '13000', 'CSLF_ID': '08123', 'Area_SF': '5431'}}
How would I do that? I have tried the following
print(cslfJson['OBJECTID'])
>>>KeyError: 'OBJECTID'
print(cslfJson['fieldAliases'['OBJECTID']])
>>>TypeError: string indices must be integers
print(cslfJson['fieldAliases'{'OBJECTID'}])
>>>SyntaxError: invalid syntax
etc... What am I doing wrong here?
You need to treat it as dict inside a dict
>>> cslfJson = {'displayFieldName': 'CSLF_ID', 'fieldValues': {'OBJECTID': '13000', 'CSLF_ID': '08123', 'Area_SF': '5431'}}
>>> print(cslfJson['fieldValues']['OBJECTID'])
13000
>>> print(cslfJson['fieldValues']['CSLF_ID'])
08123
cheers.
I'm very new in python (I usually write in php). I want to understand how to store information in an associative array, and if you can explain me whats the difference of "tuples", "arrays", "dictionary" and "list" will be wonderful (I tried to read different source but I still not caching it).
So This is my code:
#!/usr/bin/python3.4
import csv
import string
nidless_keys = dict()
nidless_keys = ['test_string1','test_string2'] #this contain the string to
# be searched in linesreader
data = {'type':[],'id':[]} #here I want to store my information
with open('path/to/csv/file.csv',newline="") as csvfile:
linesreader = csv.reader(csvfile,delimiter=',',quotechar="|")
for row in linesreader: #every line in this csv have a url like
#www.test.com/?test_string1&id=123456
current_row_string = str(row)
for needle in nidless_keys:
current_needle = str(needle)
if current_needle in current_row_string:
data[current_needle[current_row_string[-8:]]) += 1 # also I
#need to count per every id how much rows there are.
In conclusion:
my_data_stored = [current_needle][current_row_string[-8]]
current_row_string[-8] is a url which the last 8 digit of the url is an ID.
So the array should looks like this at the end of the script:
test_string1 = 123456 = 20
= 256468 = 15
test_string2 = 123155 = 10
Edit 1:
Which type I need here to store the information?
Can you tell me how to resolve this script?
It seems you want to count how many times an ID in combination with a test string occurs.
There can be multiple ID/count combinations associated with every test string.
This suggests that you should use a dictionary indexed by the test strings to store the results. In that dictionary I would suggest to store collections.Counter objects.
This way, you would have to add a special case when a key in the results dictionary isn't found to add an empty Counter. This is a common problem, so there is a specialized form of dictionary in the collections module called defaultdict.
import collections
import csv
# Using a tuple for the keys so it cannot be accidentally modified
keys = ('test_string1', 'test_string2')
result = collections.defaultdict(collections.Counter)
with open('path/to/csv/file.csv',newline="") as csvfile:
linesreader = csv.reader(csvfile,delimiter=',',quotechar="|")
for row in linesreader:
for key in keys:
if key in row:
id = row[-6:] # ID's are six digits in your example.
# The first index is into the dict, the second into the Counter.
result[key][id] += 1
There is an even easier way, by using regular expressions.
Since you seem to treat every row in a CSV file as a string, there is little need to use the CSV reader, so I'll just read the whole file as text.
import re
with open('path/to/csv/file.csv') as datafile:
text = datafile.read()
pattern = r'\?(.*)&id=(\d+)'
The pattern is a regular expression. This is a large topic in and of itself, so I'll only cover briefly what it does. (You might also want to check out the relevant HOWTO) At first glance it looks like complete gibberish, but it is actually a complete language.
In looks for two things in a line. Anything between ? and &id=, and a sequence of digits after &id=.
I'll be using IPython to give an example.
(If you don't know it, check out IPython. It is great for trying things and see if they work.)
In [1]: import re
In [2]: pattern = r'\?(.*)&id=(\d+)'
In [3]: text = """www.test.com/?test_string1&id=123456
....: www.test.com/?test_string1&id=123456
....: www.test.com/?test_string1&id=234567
....: www.test.com/?foo&id=234567
....: www.test.com/?foo&id=123456
....: www.test.com/?foo&id=1234
....: www.test.com/?foo&id=1234
....: www.test.com/?foo&id=1234"""
The text variable points to the string which is a mock-up for the contents of your CSV file.
I am assuming that:
every URL is on its own line
ID's are a sequence of digits.
If these assumptions are wrong, this won't work.
Using findall to extract every match of the pattern from the text.
In [4]: re.findall(pattern, test)
Out[4]:
[('test_string1', '123456'),
('test_string1', '123456'),
('test_string1', '234567'),
('foo', '234567'),
('foo', '123456'),
('foo', '1234'),
('foo', '1234'),
('foo', '1234')]
The findall function returns a list of 2-tuples (that is key, ID pairs). Now we just need to count those.
In [5]: import collections
In [6]: result = collections.defaultdict(collections.Counter)
In [7]: intermediate = re.findall(pattern, test)
Now we fill the result dict from the list of matches that is the intermediate result.
In [8]: for key, id in intermediate:
....: result[key][id] += 1
....:
In [9]: print(result)
defaultdict(<class 'collections.Counter'>, {'foo': Counter({'1234': 3, '123456': 1, '234567': 1}), 'test_string1': Counter({'123456': 2, '234567': 1})})
So the complete code would be:
import collections
import re
with open('path/to/csv/file.csv') as datafile:
text = datafile.read()
result = collections.defaultdict(collections.Counter)
pattern = r'\?(.*)&id=(\d+)'
intermediate = re.findall(pattern, test)
for key, id in intermediate:
result[key][id] += 1
This approach has two advantages.
You don't have to know the keys in advance.
ID's are not limited to six digits.
A brief summary of the python data types you mentioned:
A dictionary is an associative array, aka hashtable.
A list is a sequence of values.
An array is essentially the same as a list, but limited to basic datatypes. My impression is that they only exists for performance reasons, don't think I've ever used one. If performance is that critical to you, you probably don't want to use python in the first place.
A tuple is a fixed-length sequence of values (whereas lists and arrays can grow).
Lets take them one by one.
Lists:
List is a very naive kind of data structure similar to arrays in other languages in terms of the way we write them like:
['a','b','c']
This is a list in python , but seems very similar to array structure.
However there is a very large difference in the way lists are used in python and the usual arrays.
Lists are heterogenous in nature. This means that we can store any kind of data simultaneously inside it like:
ls = [1,2,'a','g',True]
As you can see, we have various kinds of data within a list and is a valid list.
However, one important thing about them is that we can access the list items using zero based indices. So we can write:
print ls[0],ls[3]
output: 1 g
Dictionary:
This datastructure is similar to a hash map data structure. It contains a (key,Value) pair. An empty dictionary looks like:
dc = {}
Now, to store a key,value pair, e.g., ('potato',3),(tomato,5), we can do as:
dc['potato'] = 3
dc['tomato'] = 5
and we saved the data in the dictionary dc.
The important thing is that we can even store another data structure element like a list within a dictionary like:
dc['list1'] = ls , where ls is the list defined above.
This shows the power of using dictionary.
In your case, you have difined a dictionary like this:
data = {'type':[],'id':[]}
This means that your dictionary will consist of only two keys and each key corresponds to a list, which are empty for now.
Talking a bit about your script, the expression :
current_row_string[-8:]
doesn't make a sense. The index should have been -6 instead of -8 that would give you the id part of the current row.
This part is the id and should have been stored in a variable say :
id = current_row_string[-6:]
Further action can be performed as seen the answer given by Roland.
list_color=['Red','Blue','Green']
for i ,b in enumerate(list_color,1):
if i<=2:
dict ={b:i}
else:
break
i+=1
print(dict)
Output:
{'Green':3}
You told interpreter to reassign name dict with new value, not to update a dict.
dict = {b:i} # we talk about this line
For creating objects based on another iterable, comprehensions are typical way to go, in this case a dictionary comprehension:
colors = ['Red','Blue','Green']
d = {color: idx for idx, color in enumerate(colors, 1)}
# {'Blue': 2, 'Green': 3, 'Red': 1}
Order is not kept, because dictionaries are unordered data structure.
Also, try to avoid naming your objects based on builtins, when dict name is used, it shadows dict builtin function.
I'm not sure why you have so many statements in the for loop, so I'm giving a simple example:
list_color=['Red','Blue','Green']
dict={}
for i ,b in enumerate(list_color,1):
dict[b] = i
print(dict)
Please note, how I define dict to be an empty dictionary before the loop. The other thing I changed is the way you assign values to the dictionary. You were overwriting the complete content of the dictionary with each assignment. I'm showing now how to add values to the dictionary.
I recommend a site like http://www.pythontutor.com/visualize.html which allows to to visualize the execution of the code. Then you can see what's going on/wrong/not according to your expectations.
I want to add string dictionary keys like this:
x = "%s-%s-%s %s:%s:00"%(dt.year,dt.month,dt.day,dt.hour,dt.minute)
dict[x] +=a1
But it gives me an error like this:
KeyError: '2015-11-26 8:47:00'
If I try print type(x) it prints str
But if i try this:
dict = {}
x = "abc"
dict[x] = 1
print dict
it print to this:
{'abc': 1}
I don't understand what is the difference.
First error is that you named your dictionary dict. That name's
already being used; it's the name of the dictionary type. Overwriting an
existing name like this is called "shadowing". Don't do it, it will mess
you up.
You're using +=. This implies that there's already a value associated
with the key, which can be incremented. If that key isn't in the dict
yet, you get a KeyError.
You probably want to set a default value of zero. This can be done in
various ways. The simplest is:
d[x] = d.get(x, 0) + a1
Also see the collections standard library, which has a defaultdict
type.