NumPy for MATLAB users (轉載）

07-22

NumPy for MATLAB users

Help

MATLAB/Octave	Python	Description
`dochelp -i % browse with Info`	`help()`	Browse help interactively
`help help`or`doc doc`	`help`	Help on using help
`help plot`	`help(plot)`or`?plot`	Help for a function
`help splines`or`doc splines`	`help(pylab)`	Help for a toolbox/library package
`demo`		Demonstration examples

Searching available documentation

MATLAB/Octave	Python	Description
`lookfor plot`		Search help files
`help`	`help(); modules [Numeric]`	List available packages
`which plot`	`help(plot)`	Locate functions

Using interactively

MATLAB/Octave	Python	Description
`octave -q`	`ipython -pylab`	Start session
`TAB`or`M-?`	`TAB`	Auto completion
`foo(.m)`	`execfile("foo.py")`or`run foo.py`	Run code from file
`history`	`hist -n`	Command history
`diary on [..] diary off`		Save command history
`exit`or`quit`	`CTRL-DCTRL-Z # windowssys.exit()`	End session

Operators

MATLAB/Octave	Python	Description
`help -`		Help on operator syntax

Arithmetic operators

MATLAB/Octave	Python	Description
`a=1; b=2;`	`a=1; b=1`	Assignment; defining a number
`a + b`	`a + b`or`add(a,b)`	Addition
`a - b`	`a - b`or`subtract(a,b)`	Subtraction
`a * b`	`a * b`or`multiply(a,b)`	Multiplication
`a / b`	`a / b`or`divide(a,b)`	Division
`a .^ b`	`a ** bpower(a,b)pow(a,b)`	Power, $a^b$
`rem(a,b)`	`a % bremainder(a,b)fmod(a,b)`	Remainder
`a+=1`	`a+=b`or`add(a,b,a)`	In place operation to save array creation overhead
`factorial(a)`		Factorial, $n!$

Relational operators

MATLAB/Octave	Python	Description
`a == b`	`a == b`or`equal(a,b)`	Equal
`a < b`	`a < b`or`less(a,b)`	Less than
`a > b`	`a > b`or`greater(a,b)`	Greater than
`a <= b`	`a <= b`or`less_equal(a,b)`	Less than or equal
`a >= b`	`a >= b`or`greater_equal(a,b)`	Greater than or equal
`a ~= b`	`a != b`or`not_equal(a,b)`	Not Equal

Logical operators

MATLAB/Octave	Python	Description
`a && b`	`a and b`	Short-circuit logical AND
`a \|\| b`	`a or b`	Short-circuit logical OR
`a & b`or`and(a,b)`	`logical_and(a,b)`or`a and b`	Element-wise logical AND
`a \| b`or`or(a,b)`	`logical_or(a,b)`or`a or b`	Element-wise logical OR
`xor(a, b)`	`logical_xor(a,b)`	Logical EXCLUSIVE OR
`~a`or`not(a)~a`or`!a`	`logical_not(a)`or`not a`	Logical NOT
`any(a)`		True if any element is nonzero
`all(a)`		True if all elements are nonzero

root and logarithm

MATLAB/Octave	Python	Description
`sqrt(a)`	`math.sqrt(a)`	Square root
`log(a)`	`math.log(a)`	Logarithm, base $e$ (natural)
`log10(a)`	`math.log10(a)`	Logarithm, base 10
`log2(a)`	`math.log(a, 2)`	Logarithm, base 2 (binary)
`exp(a)`	`math.exp(a)`	Exponential function

Round off

MATLAB/Octave	Python	Description
`round(a)`	`around(a)`or`math.round(a)`	Round
`ceil(a)`	`ceil(a)`	Round up
`floor(a)`	`floor(a)`	Round down
`fix(a)`	`fix(a)`	Round towards zero

Mathematical constants

MATLAB/Octave	Python	Description
`pi`	`math.pi`	$/pi=3.141592$
`exp(1)`	`math.e`or`math.exp(1)`	$e=2.718281$

Missing values; IEEE-754 floating point status flags

MATLAB/Octave	Python	Description
`NaN`	`nan`	Not a Number
`Inf`	`inf`	Infinity, $/infty$
	`plus_inf`	Infinity, $+/infty$
	`minus_inf`	Infinity, $-/infty$
	`plus_zero`	Plus zero, $+0$
	`minus_zero`	Minus zero, $-0$

Complex numbers

MATLAB/Octave	Python	Description
`i`	`z = 1j`	Imaginary unit
`z = 3+4i`	`z = 3+4j`or`z = complex(3,4)`	A complex number, $3+4i$
`abs(z)`	`abs(3+4j)`	Absolute value (modulus)
`real(z)`	`z.real`	Real part
`imag(z)`	`z.imag`	Imaginary part
`arg(z)`		Argument
`conj(z)`	`z.conj(); z.conjugate()`	Complex conjugate

Trigonometry

MATLAB/Octave	Python	Description
`atan(a,b)`	`atan2(b,a)`	Arctangent, $/arctan(b/a)$
	`hypot(x,y)`	Hypotenus; Euclidean distance

Generate random numbers

MATLAB/Octave	Python	Description
`rand(1,10)`	`random.random((10,))random.uniform((10,))`	Uniform distribution
`2+5*rand(1,10)`	`random.uniform(2,7,(10,))`	Uniform: Numbers between 2 and 7
`rand(6)`	`random.uniform(0,1,(6,6))`	Uniform: 6,6 array
`randn(1,10)`	`random.standard_normal((10,))`	Normal distribution

Vectors

MATLAB/Octave	Python	Description
`a=[2 3 4 5];`	`a=array([2,3,4,5])`	Row vector, $1 /times n$-matrix
`adash=[2 3 4 5]";`	`array([2,3,4,5])[:,NewAxis]array([2,3,4,5]).reshape(-1,1)r_[1:10,"c"]`	Column vector, $m /times 1$-matrix

Sequences

MATLAB/Octave	Python	Description
`1:10`	`arange(1,11, dtype=Float)range(1,11)`	1,2,3, ... ,10
`0:9`	`arange(10.)`	0.0,1.0,2.0, ... ,9.0
`1:3:10`	`arange(1,11,3)`	1,4,7,10
`10:-1:1`	`arange(10,0,-1)`	10,9,8, ... ,1
`10:-3:1`	`arange(10,0,-3)`	10,7,4,1
`linspace(1,10,7)`	`linspace(1,10,7)`	Linearly spaced vector of n=7 points
`reverse(a)`	`a[::-1]`or	Reverse
`a(:) = 3`	`a.fill(3), a[:] = 3`	Set all values to same scalar value

Concatenation (vectors)

MATLAB/Octave	Python	Description
`[a a]`	`concatenate((a,a))`	Concatenate two vectors
`[1:4 a]`	`concatenate((range(1,5),a), axis=1)`

Repeating

MATLAB/Octave	Python	Description
`[a a]`	`concatenate((a,a))`	1 2 3, 1 2 3
	`a.repeat(3)`or	1 1 1, 2 2 2, 3 3 3
	`a.repeat(a)`or	1, 2 2, 3 3 3

Miss those elements out

MATLAB/Octave	Python	Description
`a(2:end)`	`a[1:]`	miss the first element
`a([1:9])`		miss the tenth element
`a(end)`	`a[-1]`	last element
`a(end-1:end)`	`a[-2:]`	last two elements

Maximum and minimum

MATLAB/Octave	Python	Description
`max(a,b)`	`maximum(a,b)`	pairwise max
`max([a b])`	`concatenate((a,b)).max()`	max of all values in two vectors
`[v,i] = max(a)`	`v,i = a.max(0),a.argmax(0)`

Vector multiplication

MATLAB/Octave	Python	Description
`a.*a`	`a*a`	Multiply two vectors
`dot(u,v)`	`dot(u,v)`	Vector dot product, $u /cdot v$

Matrices

MATLAB/Octave	Python	Description
`a = [2 3;4 5]`	`a = array([[2,3],[4,5]])`	Define a matrix

Concatenation (matrices); rbind and cbind

MATLAB/Octave	Python	Description
`[a ; b]`	`concatenate((a,b), axis=0)vstack((a,b))`	Bind rows
`[a , b]`	`concatenate((a,b), axis=1)hstack((a,b))`	Bind columns
	`concatenate((a,b), axis=2)dstack((a,b))`	Bind slices (three-way arrays)
`[a(:), b(:)]`	`concatenate((a,b), axis=None)`	Concatenate matrices into one vector
`[1:4 ; 1:4]`	`concatenate((r_[1:5],r_[1:5])).reshape(2,-1)vstack((r_[1:5],r_[1:5]))`	Bind rows (from vectors)
`[1:4 ; 1:4]"`		Bind columns (from vectors)

Array creation

MATLAB/Octave	Python	Description
`zeros(3,5)`	`zeros((3,5),Float)`	0 filled array
	`zeros((3,5))`	0 filled array of integers
`ones(3,5)`	`ones((3,5),Float)`	1 filled array
`ones(3,5)*9`		Any number filled array
`eye(3)`	`identity(3)`	Identity matrix
`diag([4 5 6])`	`diag((4,5,6))`	Diagonal
`magic(3)`		Magic squares; Lo Shu
	`a = empty((3,3))`	Empty array

Reshape and flatten matrices

MATLAB/Octave	Python	Description
`reshape(1:6,3,2)";`	`arange(1,7).reshape(2,-1)a.setshape(2,3)`	Reshaping (rows first)
`reshape(1:6,2,3);`	`arange(1,7).reshape(-1,2).transpose()`	Reshaping (columns first)
`a"(:)`	`a.flatten()`or	Flatten to vector (by rows, like comics)
`a(:)`	`a.flatten(1)`	Flatten to vector (by columns)
`vech(a)`		Flatten upper triangle (by columns)

Shared data (slicing)

MATLAB/Octave	Python	Description
`b = a`	`b = a.copy()`	Copy of a

Indexing and accessing elements (Python: slicing)

MATLAB/Octave	Python	Description
`a = [ 11 12 13 14 ...21 22 23 24 ...31 32 33 34 ]`	`a = array([[ 11, 12, 13, 14 ],[ 21, 22, 23, 24 ],[ 31, 32, 33, 34 ]])`	Input is a 3,4 array
`a(2,3)`	`a[1,2]`	Element 2,3 (row,col)
`a(1,:)`	`a[0,]`	First row
`a(:,1)`	`a[:,0]`	First column
`a([1 3],[1 4]);`	`a.take([0,2]).take([0,3], axis=1)`	Array as indices
`a(2:end,:)`	`a[1:,]`	All, except first row
`a(end-1:end,:)`	`a[-2:,]`	Last two rows
`a(1:2:end,:)`	`a[::2,:]`	Strides: Every other row
	`a[...,2]`	Third in last dimension (axis)
`a(:,[1 3 4])`	`a.take([0,2,3],axis=1)`	Remove one column
	`a.diagonal(offset=0)`	Diagonal

Assignment

MATLAB/Octave	Python	Description
`a(:,1) = 99`	`a[:,0] = 99`
`a(:,1) = [99 98 97]"`	`a[:,0] = array([99,98,97])`
`a(a>90) = 90;`	`(a>90).choose(a,90)a.clip(min=None, max=90)`	Clipping: Replace all elements over 90
	`a.clip(min=2, max=5)`	Clip upper and lower values

Transpose and inverse

MATLAB/Octave	Python	Description
`a"`	`a.conj().transpose()`	Transpose
`a."`or`transpose(a)`	`a.transpose()`	Non-conjugate transpose
`det(a)`	`linalg.det(a)`or	Determinant
`inv(a)`	`linalg.inv(a)`or	Inverse
`pinv(a)`	`linalg.pinv(a)`	Pseudo-inverse
`norm(a)`	`norm(a)`	Norms
`eig(a)`	`linalg.eig(a)[0]`	Eigenvalues
`svd(a)`	`linalg.svd(a)`	Singular values
`chol(a)`	`linalg.cholesky(a)`	Cholesky factorization
`[v,l] = eig(a)`	`linalg.eig(a)[1]`	Eigenvectors
`rank(a)`	`rank(a)`	Rank

Sum

MATLAB/Octave	Python	Description
`sum(a)`	`a.sum(axis=0)`	Sum of each column
`sum(a")`	`a.sum(axis=1)`	Sum of each row
`sum(sum(a))`	`a.sum()`	Sum of all elements
	`a.trace(offset=0)`	Sum along diagonal
`cumsum(a)`	`a.cumsum(axis=0)`	Cumulative sum (columns)

Sorting

MATLAB/Octave	Python	Description
`a = [ 4 3 2 ; 2 8 6 ; 1 4 7 ]`	`a = array([[4,3,2],[2,8,6],[1,4,7]])`	Example data
`sort(a(:))`	`a.ravel().sort()`or	Flat and sorted
`sort(a)`	`a.sort(axis=0)`or`msort(a)`	Sort each column
`sort(a")"`	`a.sort(axis=1)`	Sort each row
`sortrows(a,1)`	`a[a[:,0].argsort(),]`	Sort rows (by first row)
	`a.ravel().argsort()`	Sort, return indices
	`a.argsort(axis=0)`	Sort each column, return indices
	`a.argsort(axis=1)`	Sort each row, return indices

Maximum and minimum

MATLAB/Octave	Python	Description
`max(a)`	`a.max(0)`or`amax(a [,axis=0])`	max in each column
`max(a")`	`a.max(1)`or`amax(a, axis=1)`	max in each row
`max(max(a))`	`a.max()`or	max in array
`[v i] = max(a)`		return indices, i
`max(b,c)`	`maximum(b,c)`	pairwise max
`cummax(a)`
	`a.ptp(); a.ptp(0)`	max-to-min range

Matrix manipulation

MATLAB/Octave	Python	Description
`fliplr(a)`	`fliplr(a)`or`a[:,::-1]`	Flip left-right
`flipud(a)`	`flipud(a)`or`a[::-1,]`	Flip up-down
`rot90(a)`	`rot90(a)`	Rotate 90 degrees
`repmat(a,2,3)kron(ones(2,3),a)`	`kron(ones((2,3)),a)`	Repeat matrix: [ a a a ; a a a ]
`triu(a)`	`triu(a)`	Triangular, upper
`tril(a)`	`tril(a)`	Triangular, lower

Equivalents to "size"

MATLAB/Octave	Python	Description
`size(a)`	`a.shape`or`a.getshape()`	Matrix dimensions
`size(a,2)`or`length(a)`	`a.shape[1]`or`size(a, axis=1)`	Number of columns
`length(a(:))`	`a.size`or`size(a[, axis=None])`	Number of elements
`ndims(a)`	`a.ndim`	Number of dimensions
	`a.nbytes`	Number of bytes used in memory

Matrix- and elementwise- multiplication

MATLAB/Octave	Python	Description
`a .* b`	`a * b`or`multiply(a,b)`	Elementwise operations
`a * b`	`matrixmultiply(a,b)`	Matrix product (dot product)
	`inner(a,b)`or	Inner matrix vector multiplication $a/cdot b"$
	`outer(a,b)`or	Outer product
`kron(a,b)`	`kron(a,b)`	Kronecker product
`a / b`		Matrix division, $b{/cdot}a^{-1}$
`a / b`	`linalg.solve(a,b)`	Left matrix division, $b^{-1}{/cdot}a$ /newline (solve linear equations)
	`vdot(a,b)`	Vector dot product
	`cross(a,b)`	Cross product

Find; conditional indexing

MATLAB/Octave	Python	Description
`find(a)`	`a.ravel().nonzero()`	Non-zero elements, indices
`[i j] = find(a)`	`(i,j) = a.nonzero()(i,j) = where(a!=0)`	Non-zero elements, array indices
`[i j v] = find(a)`	`v = a.compress((a!=0).flat)v = extract(a!=0,a)`	Vector of non-zero values
`find(a>5.5)`	`(a>5.5).nonzero()`	Condition, indices
	`a.compress((a>5.5).flat)`	Return values
`a .* (a>5.5)`	`where(a>5.5,0,a)`or`a * (a>5.5)`	Zero out elements above 5.5
	`a.put(2,indices)`	Replace values

Multi-way arrays

MATLAB/Octave	Python	Description
`a = cat(3, [1 2; 1 2],[3 4; 3 4]);`	`a = array([[[1,2],[1,2]], [[3,4],[3,4]]])`	Define a 3-way array
`a(1,:,:)`	`a[0,...]`

File input and output

MATLAB/Octave	Python	Description
`f = load("data.txt")`	`f = fromfile("data.txt")f = load("data.txt")`	Reading from a file (2d)
`f = load("data.txt")`	`f = load("data.txt")`	Reading from a file (2d)
`x = dlmread("data.csv", ";")`	`f = load("data.csv", delimiter=";")`	Reading fram a CSV file (2d)
`save -ascii data.txt f`	`save("data.csv", f, fmt="%.6f", delimiter=";")`	Writing to a file (2d)
	`f.tofile(file="data.csv", format="%.6f", sep=";")`	Writing to a file (1d)
	`f = fromfile(file="data.csv", sep=";")`	Reading from a file (1d)

PlottingBasic x-y plots

MATLAB/Octave	Python	Description
`plot(a)`	`plot(a)`	1d line plot
`plot(x(:,1),x(:,2),"o")`	`plot(x[:,0],x[:,1],"o")`	2d scatter plot
`plot(x1,y1, x2,y2)`	`plot(x1,y1,"bo", x2,y2,"go")`	Two graphs in one plot
`plot(x1,y1)hold onplot(x2,y2)`	`plot(x1,y1,"o")plot(x2,y2,"o")show() # as normal`	Overplotting: Add new plots to current
`subplot(211)`	`subplot(211)`	subplots
`plot(x,y,"ro-")`	`plot(x,y,"ro-")`	Plotting symbols and color

Axes and titles

MATLAB/Octave	Python	Description
`grid on`	`grid()`	Turn on grid lines
`axis equalaxis("equal")replot`	`figure(figsize=(6,6))`	1:1 aspect ratio
`axis([ 0 10 0 5 ])`	`axis([ 0, 10, 0, 5 ])`	Set axes manually
`title("title")xlabel("x-axis")ylabel("y-axis")`		Axis labels and titles
	`text(2,25,"hello")`	Insert text

Log plots

MATLAB/Octave	Python	Description
`semilogy(a)`	`semilogy(a)`	logarithmic y-axis
`semilogx(a)`	`semilogx(a)`	logarithmic x-axis
`loglog(a)`	`loglog(a)`	logarithmic x and y axes

Filled plots and bar plots

MATLAB/Octave	Python	Description
`fill(t,s,"b", t,c,"g")% fill has a bug?`	`fill(t,s,"b", t,c,"g", alpha=0.2)`	Filled plot

Functions

MATLAB/Octave	Python	Description
`f = inline("sin(x/3) - cos(x/5)")`		Defining functions
`ezplot(f,[0,40])fplot("sin(x/3) - cos(x/5)",[0,40])% no ezplot`	`x = arrayrange(0,40,.5)y = sin(x/3) - cos(x/5)plot(x,y, "o")`	Plot a function for given range

Polar plots

MATLAB/Octave	Python	Description
`theta = 0:.001:2pi;r = sin(2theta);`	`theta = arange(0,2pi,0.001)r = sin(2theta)`
`polar(theta, rho)`	`polar(theta, rho)`

Histogram plots

MATLAB/Octave	Python	Description
`hist(randn(1000,1))`
`hist(randn(1000,1), -4:4)`
`plot(sort(a))`

3d dataContour and image plots

MATLAB/Octave	Python	Description
`contour(z)`	`levels, colls = contour(Z, V,origin="lower", extent=(-3,3,-3,3))clabel(colls, levels, inline=1,fmt="%1.1f", fontsize=10)`	Contour plot
`contourf(z); colormap(gray)`	`contourf(Z, V,cmap=cm.gray,origin="lower",extent=(-3,3,-3,3))`	Filled contour plot
`image(z)colormap(gray)`	`im = imshow(Z,interpolation="bilinear",origin="lower",extent=(-3,3,-3,3))`	Plot image data
	`# imshow() and contour() as above`	Image with contours
`quiver()`	`quiver()`	Direction field vectors

Perspective plots of surfaces over the x-y plane

MATLAB/Octave	Python	Description
`n=-2:.1:2;[x,y] = meshgrid(n,n);z=x.*exp(-x.^2-y.^2);`	`n=arrayrange(-2,2,.1)[x,y] = meshgrid(n,n)z = xpower(math.e,-x2-y*2)`
`mesh(z)`		Mesh plot
`surf(x,y,z)`or`surfl(x,y,z)% no surfl()`		Surface plot

Scatter (cloud) plots

MATLAB/Octave	Python	Description
`plot3(x,y,z,"k+")`		3d scatter plot

Save plot to a graphics file

MATLAB/Octave	Python	Description
`plot(1:10)print -depsc2 foo.epsgset output "foo.eps"gset terminal postscript epsplot(1:10)`	`savefig("foo.eps")`	PostScript
	`savefig("foo.pdf")`	PDF
	`savefig("foo.svg")`	SVG (vector graphics for www)
`print -dpng foo.png`	`savefig("foo.png")`	PNG (raster graphics)

Data analysisSet membership operators

MATLAB/Octave	Python	Description
`a = [ 1 2 2 5 2 ];b = [ 2 3 4 ];`	`a = array([1,2,2,5,2])b = array([2,3,4])a = set([1,2,2,5,2])b = set([2,3,4])`	Create sets
`unique(a)`	`unique1d(a)unique(a)set(a)`	Set unique
`union(a,b)`	`union1d(a,b)a.union(b)`	Set union
`intersect(a,b)`	`intersect1d(a)a.intersection(b)`	Set intersection
`setdiff(a,b)`	`setdiff1d(a,b)a.difference(b)`	Set difference
`setxor(a,b)`	`setxor1d(a,b)a.symmetric_difference(b)`	Set exclusion
`ismember(2,a)`	`2 in asetmember1d(2,a)contains(a,2)`	True for set member

Statistics

MATLAB/Octave	Python	Description
`mean(a)`	`a.mean(axis=0)mean(a [,axis=0])`	Average
`median(a)`	`median(a)`or`median(a [,axis=0])`	Median
`std(a)`	`a.std(axis=0)`or`std(a [,axis=0])`	Standard deviation
`var(a)`	`a.var(axis=0)`or`var(a)`	Variance
`corr(x,y)`	`correlate(x,y)`or`corrcoef(x,y)`	Correlation coefficient
`cov(x,y)`	`cov(x,y)`	Covariance

Interpolation and regression

MATLAB/Octave	Python	Description
`z = polyval(polyfit(x,y,1),x)plot(x,y,"o", x,z ,"-")`	`(a,b) = polyfit(x,y,1)plot(x,y,"o", x,a*x+b,"-")`	Straight line fit
`a = x/y`	`linalg.lstsq(x,y)`	Linear least squares $y = ax + b$
`polyfit(x,y,3)`	`polyfit(x,y,3)`	Polynomial fit

Non-linear methodsPolynomials, root finding

MATLAB/Octave	Python	Description
	`poly()`	Polynomial
`roots([1 -1 -1])`	`roots()`	Find zeros of polynomial
`f = inline("1/x - (x-1)")fzero(f,1)`		Find a zero near $x = 1$
`solve("1/x = x-1")`		Solve symbolic equations
`polyval([1 2 1 2],1:10)`	`polyval(array([1,2,1,2]),arange(1,11))`	Evaluate polynomial

Differential equations

MATLAB/Octave	Python	Description
`diff(a)`	`diff(x, n=1, axis=0)`	Discrete difference function and approximate derivative
		Solve differential equations

Fourier analysis

MATLAB/Octave	Python	Description
`fft(a)`	`fft(a)`or	Fast fourier transform
`ifft(a)`	`ifft(a)`or	Inverse fourier transform
	`convolve(x,y)`	Linear convolution

Symbolic algebra; calculus

MATLAB/Octave	Python	Description
`factor()`		Factorization

Programming

MATLAB/Octave	Python	Description
`.m`	`.py`	Script file extension
`%%`or`#`	`#`	Comment symbol (rest of line)
`% must be in MATLABPATH% must be in LOADPATH`	`from pylab import *`	Import library functions
`string="a=234";eval(string)`	`string="a=234"eval(string)`	Eval

Loops

MATLAB/Octave	Python	Description
`for i=1:5; disp(i); end`	`for i in range(1,6): print(i)`	for-statement
`for i=1:5disp(i)disp(i*2)end`	`for i in range(1,6):print(i)print(i*2)`	Multiline for statements

Conditionals

MATLAB/Octave	Python	Description
`if 1>0 a=100; end`	`if 1>0: a=100`	if-statement
`if 1>0 a=100; else a=0; end`		if-else-statement

Debugging

MATLAB/Octave	Python	Description
`ans`		Most recent evaluated expression
`whos`or`who`		List variables loaded into memory
`clear x`or`clear [all]`		Clear variable $x$ from memory
`disp(a)`	`print a`	Print

Working directory and OS

MATLAB/Octave	Python	Description
`dir`or`ls`	`os.listdir(".")`	List files in directory
`what`	`grep.grep("*.py")`	List script files in directory
`pwd`	`os.getcwd()`	Displays the current working directory
`cd foo`	`os.chdir("foo")`	Change working directory
`!notepadsystem("notepad")`	`os.system("notepad")os.popen("notepad")`	Invoke a System Command