Debugging (displaying) SQL command sent to the db by SQLAlchemy

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I have an ORM class called Person, which wraps around a person table:

After setting up the connection to the db etc, I run the statement:

people = session.query(Person).all()

The person table does not contain any data (as yet), so when I print the variable people, I get an empty list.

I renamed the table referred to in my ORM class People, to people_foo (which does not exist).

I then run the script again. I was surprised that no exception was thrown when attempting to access a table that does not exist.

I therefore have the following 2 questions:

  1. How may I setup SQLAlchemy so that it propagates db errors back to the script?
  2. How may I view (i.e. print) the SQL that is being sent to the db engine?

If it helps, I am using PostgreSQL.


I am writing a package. In my script, I have the following code (shortened here):

import common # imports logging and defines logging setup funcs etc

logger = logging.getLogger(__name__)

def main():    
    parser = OptionParser(usage="%prog [options] <commands>",
                          version="%prog 1.0")

    commands = OptionGroup(parser, "commands")

        help="log to FILE. if not set, no logging will be done"

        metavar="LOG LEVEL",
        help="Debug level. if not set, level will default to low"

    # Set defaults if not specified
    if not options.loglevel:
        loglevel = 1
        loglevel = options.loglevel

    if not options.logfile:
        logfilename = "datafeed.log"
        logfilename = options.logfile

    common.setup_logger(False, logfilename, loglevel) 

       # and so on ...


import logging

    # not sure how to "bind" to the logger in

    engine = create_engine("postgres://postgres:[email protected]:port/dbname", echo=True)


Common module sets the logger up correctly, and I can use the logger in my other modules that import common.

However in dbfuncs module, I am getting the following error/warning:

No handlers could be found for logger "sqlalchemy.engine.base.Engine

Debugging (displaying) SQL command sent to the db by SQLAlchemy around: Questions

Removing white space around a saved image in matplotlib

2 answers

I need to take an image and save it after some process. The figure looks fine when I display it, but after saving the figure, I got some white space around the saved image. I have tried the "tight" option for savefig method, did not work either. The code:

  import matplotlib.image as mpimg
  import matplotlib.pyplot as plt

  fig = plt.figure(1)
  img = mpimg.imread(path)

  extent = ax.get_window_extent().transformed(fig.dpi_scale_trans.inverted())
  plt.savefig("1.png", bbox_inches=extent)


I am trying to draw a basic graph by using NetworkX on a figure and save it. I realized that without a graph it works, but when added a graph I get white space around the saved image;

import matplotlib.image as mpimg
import matplotlib.pyplot as plt
import networkx as nx

G = nx.Graph()
pos = {1:[100,120], 2:[200,300], 3:[50,75]}

fig = plt.figure(1)
img = mpimg.imread("image.jpg")

nx.draw(G, pos=pos)

extent = ax.get_window_extent().transformed(fig.dpi_scale_trans.inverted())
plt.savefig("1.png", bbox_inches = extent)


Answer #1

You can remove the white space padding by setting bbox_inches="tight" in savefig:


You"ll have to put the argument to bbox_inches as a string, perhaps this is why it didn"t work earlier for you.

Possible duplicates:

Matplotlib plots: removing axis, legends and white spaces

How to set the margins for a matplotlib figure?

Reduce left and right margins in matplotlib plot


Answer #2

I cannot claim I know exactly why or how my “solution” works, but this is what I had to do when I wanted to plot the outline of a couple of aerofoil sections — without white margins — to a PDF file. (Note that I used matplotlib inside an IPython notebook, with the -pylab flag.)

plt.subplots_adjust(top = 1, bottom = 0, right = 1, left = 0, 
            hspace = 0, wspace = 0)
plt.savefig("filename.pdf", bbox_inches = "tight",
    pad_inches = 0)

I have tried to deactivate different parts of this, but this always lead to a white margin somewhere. You may even have modify this to keep fat lines near the limits of the figure from being shaved by the lack of margins.

Debugging (displaying) SQL command sent to the db by SQLAlchemy log: Questions


Python"s equivalent of && (logical-and) in an if-statement

5 answers

delete By delete

Here"s my code:

def front_back(a, b):
  # +++your code here+++
  if len(a) % 2 == 0 && len(b) % 2 == 0:
    return a[:(len(a)/2)] + b[:(len(b)/2)] + a[(len(a)/2):] + b[(len(b)/2):] 
    #todo! Not yet done. :P

I"m getting an error in the IF conditional.
What am I doing wrong?


Answer #1

You would want and instead of &&.


Answer #2

Python uses and and or conditionals.


if foo == "abc" and bar == "bac" or zoo == "123":
  # do something


How do you get the logical xor of two variables in Python?

5 answers

Zach Hirsch By Zach Hirsch

How do you get the logical xor of two variables in Python?

For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string):

str1 = raw_input("Enter string one:")
str2 = raw_input("Enter string two:")
if logical_xor(str1, str2):
    print "ok"
    print "bad"

The ^ operator seems to be bitwise, and not defined on all objects:

>>> 1 ^ 1
>>> 2 ^ 1
>>> "abc" ^ ""
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for ^: "str" and "str"

Answer #1

If you"re already normalizing the inputs to booleans, then != is xor.

bool(a) != bool(b)


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