3

I have the following code:

var_one = var_two[var_three-1]
var_one = "string_one" + var_1

And I need to do the following to it:

var_four = 'string_two', var_one

However, this returns the following error:

TypeError: Can't convert 'tuple' object to str implicity

I have tried things such as str(var_one) and using strip but these did not work. What can I do to achieve the result I require?

EDIT - Here are what the variables contain:

var_one: new variable

var_two: tuple

var_three: integer

var_four: new

EDIT2:

The line in the program that makes the error is: os.system(var_four)

Eden Crow
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5 Answers5

4
one_big_string = ''.join(tuple)   
print one_big_string
Katriel
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prelic
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3

What you've written is fine:

>>> x = 1
>>> y = 1, x
>>>

The problem is that somewhere else in your code, you're using var_four as a string where it should be a tuple.

BTW, I think it's neater to put parentheses around tuples like this; otherwise I tend to think they're being used in tuple unpacking.

EDIT: There are all sorts of ways to join and format strings -- Python is good at that. In somewhat-decreasing order of generality:

"{first_thing} {second_thing}".format(first_thing=var_one, second_thing=var_two)

"{0} {1}".format(var_one, var_two)

var_one + var_two
Katriel
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  • I need var_four to be a string, that is my problem. – Eden Crow Feb 24 '12 at 19:27
  • Updated the question with the line that is causing the error. – Eden Crow Feb 24 '12 at 19:35
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    @EdenCrow: It's not a string. You __defined__ it not to be a string. It's a tuple. You can _convert_ it to a string in any number of ways, depending on how you want it converted. – Katriel Feb 24 '12 at 19:36
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    @EdenCrow it looks like you want `"".join(var_four)` i.e. you want to concatenate the elements -- but then `subprocess.Popen` is the recommended way to call external programs from Python. – Katriel Feb 24 '12 at 19:37
  • So using the `,` in variable assignment causes it to become a tuple? Then how do I make a string from adding `string_two` and `var_one` together? EDIT: Ninja'd - will have a look at `"".join(var_four)` – Eden Crow Feb 24 '12 at 19:38
  • @katrielalex Please move your responses into the answer. – Edwin Feb 24 '12 at 19:43
2

Your code looks fine as is.

Try running import pdb; pdb.set_trace() in your program to see if you can find the line triggering the error.

EDIT: You'll want to use ''.join(var_four) to convert var_four into a string before adding it to whatever it is you want to use it. Please note that this will actually create a new string and not overwrite var_four. See Python 3 string.join() equivalent?

Also, you should be using the subprocess module instead of os.system. See the Python 3.x documentation.

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Edwin
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0
str(my_tuple)

This seems too easy, but this works in Python 3.6

>>> x = list(range(100))
>>> y = list(range(500, 600))
>>> zip_obj = zip(x, y)
>>> my_tuple = tuple(zip_obj)
>>> type(my_tuple)
>>> <class 'tuple'>
>>> tuple_str = str(my_tuple)
>>> tuple_str
'((0, 500), (1, 501), (2, 502), (3, 503), (4, 504), (5, 505), (6, 506), (7, 507), (8, 508), (9, 509), (10, 510), (11, 511), (12, 512), (13, 513), (14, 514), (15, 515), (16, 516), (17, 517), (18, 518), (19, 519), (20, 520), (21, 521), (22, 522), (23, 523), (24, 524), (25, 525), (26, 526), (27, 527), (28, 528), (29, 529), (30, 530), (31, 531), (32, 532), (33, 533), (34, 534), (35, 535), (36, 536), (37, 537), (38, 538), (39, 539), (40, 540), (41, 541), (42, 542), (43, 543), (44, 544), (45, 545), (46, 546), (47, 547), (48, 548), (49, 549), (50, 550), (51, 551), (52, 552), (53, 553), (54, 554), (55, 555), (56, 556), (57, 557), (58, 558), (59, 559), (60, 560), (61, 561), (62, 562), (63, 563), (64, 564), (65, 565), (66, 566), (67, 567), (68, 568), (69, 569), (70, 570), (71, 571), (72, 572), (73, 573), (74, 574), (75, 575), (76, 576), (77, 577), (78, 578), (79, 579), (80, 580), (81, 581), (82, 582), (83, 583), (84, 584), (85, 585), (86, 586), (87, 587), (88, 588), (89, 589), (90, 590), (91, 591), (92, 592), (93, 593), (94, 594), (95, 595), (96, 596), (97, 597), (98, 598), (99, 599))'
>>>
Scott Skiles
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0

os.system expects a string which will will execute in the shell, but you're giving it a tuple instead.

Imagine we want to run the command rm -rf /home/mike. You might be doing something like 

binary_and_option = 'rm -rf'
directory = '/home/mike'

command = binary_and_option, directory # This is the tuple 
                                       #    ('rm -rf', '/home/mike') 
                                       # it is NOT the string 
                                       #     'rm -rf /home/mike'

os.system(command) # this clearly won't work, since it's just 
                   # os.system(('rm -rf', '/home/mike'))

what you want to do instead is 

command = "%d %d" % (binary_and_option, directory)

to assemble the string. You are probably thinking comma assembles str-ed objects together with spaces in between, but that's only for print; it's not how strings work in general.

But wait, there's more! You never want to use os.system, especially when you're going to build commands. It invokes the shell (which introduces unncessary security risks and other penalties) and has an inflexible API. Instead, use the subprocess module.

import subprocess 

binary_and_option = ['rm', '-rf']
directory = '/home/mike'

command = binary_and_option + [directory]

subprocess.call(command)
Mike Graham
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